U.S. patent number 10,431,295 [Application Number 14/291,443] was granted by the patent office on 2019-10-01 for static random access memory and method of controlling the same.
This patent grant is currently assigned to TAIWAN SEMICONDUCTOR MANUFACTURING COMPANY, LTD.. The grantee listed for this patent is TAIWAN SEMICONDUCTOR MANUFACTURING COMPANY, LTD.. Invention is credited to Yen-Huei Chen, Hung-Jen Liao, Chih-Yu Lin, Li-Wen Wang.
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United States Patent |
10,431,295 |
Wang , et al. |
October 1, 2019 |
Static random access memory and method of controlling the same
Abstract
A static random access memory (SRAM) that includes a memory cell
comprising at least two p-type pass gates. The SRAM also includes a
first data line connected to the memory cell, a second data line
connected to the memory cell and a voltage control unit connected
to the first data line, wherein the voltage control unit is
configured to control the memory cell.
Inventors: |
Wang; Li-Wen (Taichung,
TW), Lin; Chih-Yu (Taichung, TW), Chen;
Yen-Huei (Jhudong Township, TW), Liao; Hung-Jen
(Hsinchu, TW) |
Applicant: |
Name |
City |
State |
Country |
Type |
TAIWAN SEMICONDUCTOR MANUFACTURING COMPANY, LTD. |
Hsinchu |
N/A |
TW |
|
|
Assignee: |
TAIWAN SEMICONDUCTOR MANUFACTURING
COMPANY, LTD. (Hsinchu, TW)
|
Family
ID: |
54702554 |
Appl.
No.: |
14/291,443 |
Filed: |
May 30, 2014 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20150348598 A1 |
Dec 3, 2015 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G11C
11/417 (20130101); G11C 11/419 (20130101) |
Current International
Class: |
G11C
7/00 (20060101); G11C 11/417 (20060101); G11C
11/419 (20060101) |
Field of
Search: |
;365/72 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Chen; Xiaochun L
Attorney, Agent or Firm: Hauptman Ham, LLP
Claims
What is claimed is:
1. A static random access memory (SRAM) comprising: a memory cell,
wherein the memory cell comprises at least two p-type pass gates; a
bit line connected to the memory cell; a bit line bar connected to
the memory cell; a word line connected to the memory cell; an
n-type transistor connected between a ground voltage and a first
node; a first inverter having an input terminal configured to
receive a data signal and an output terminal connected to the word
line, the first inverter being connected between a supply voltage
and the first node; and a voltage control unit configured to
control the N-type transistor and to control the memory cell by
providing an operating voltage on the first node which affects
operation of the first inverter and thereby causes a voltage on the
word line to undergo at least a double transition including a first
transition to the ground voltage and then a second transition to an
intermediate voltage which is greater than the ground voltage but
substantially lower than the supply voltage; and wherein: the
voltage control unit includes a p-type capacitor-connected
transistor connected to the first node and thereby to the word
line; and the voltage control unit is further configured to
selectively adjust voltages correspondingly of the bit line and the
bit line bar.
2. The SRAM of claim 1, wherein each p-type pass gate of the at
least two p-type pass gates has a three-dimensional gate
structure.
3. The SRAM of claim 1, wherein: after the voltage on the word line
undergoes the second transition from the ground voltage to the
intermediate voltage, the voltage control unit is further
configured to provide the operating voltage on the first node so as
to further affect operation of the first inverter and thereby cause
the voltage on the word line to undergo a third transition from the
intermediate voltage to the ground voltage.
4. The SRAM of claim 1, wherein the voltage control unit further
includes: series-connected inverters coupled between the p-type
capacitor-connected transistor and a timing control unit.
5. The SRAM of claim 4, wherein: the voltage control unit is
further configured to provide a signal on a second node between
first and second ones of the series-connected inverters to a gate
electrode of the N-type transistor.
6. The SRAM of claim 1, wherein: the memory cell is a single-port
memory cell, a two-port memory cell or a dual-port memory cell.
7. A semiconductor device comprising: a static random access memory
(SRAM) comprising: a memory cell, wherein the memory cell comprises
at least two p-type pass gates; a bit line connected to the memory
cell; a bit line bar connected to the memory cell; a word line
connected to the memory cell; a word line driver including a first
inverter having an input configured to receive a data signal and an
output connected to the word line, the first inverter being
connected between a supply voltage and an adjustment line; a
voltage adjuster including an n-type transistor connected between a
ground voltage and the adjustment line; and a voltage control unit
connected to the memory cell, the voltage control unit being
connected to the adjustment line and connected to the bit line by a
second inverter and connected to the bit line bar by a third
inverter, wherein the voltage control unit is configured to control
the n-type transistor and to control the memory cell by providing
an operating voltage on the adjustment line which affects operation
of the first inverter and thereby causes a voltage on the word line
to undergo at least a double transition including a first
transition to the ground voltage and then a second transition to an
intermediate voltage which is greater than the ground voltage but
substantially lower than the supply voltage; and wherein the
voltage control unit includes a p-type capacitor-connected
transistor connected to the adjustment line; and the voltage
control unit is further configured to selectively adjust voltages
correspondingly of the bit line and the bit line bar.
8. The semiconductor device of claim 7, wherein the memory cell is
a single-port memory cell or a dual-port memory cell.
9. The semiconductor device of claim 7, wherein the memory cell is
a two-port memory cell.
10. The semiconductor device of claim 7, wherein each p-type pass
gate of the at least two p-type pass gates has a three-dimensional
gate structure.
11. The semiconductor device of claim 7, wherein: an output of the
second inverter is configured to drive only the bit line, and is
coupled to the bit line, and an output of the third inverter is
configured to drive only the bit line bar, and is coupled to the
bit line bar.
12. The semiconductor device of claim 7, wherein: after the voltage
on the word line undergoes the second transition from the ground
voltage to the intermediate voltage, the voltage control unit is
further configured to provide the operating voltage on the
adjustment line so as to further affect operation of the first
inverter and thereby cause the voltage on the word line to undergo
a third transition from the intermediate voltage to the ground
voltage.
13. The semiconductor device of claim 7, wherein the voltage
control unit further includes: series-connected inverters coupled
between the p-type capacitor-connected transistor and a timing
control unit.
14. The semiconductor device of claim 13, wherein: the voltage
control unit is further configured to provide a signal on a node
between first and second ones of the series-connected inverters to
a gate electrode of the N-type transistor.
15. A method of controlling a static random access memory (SRAM),
the method comprising: pre-charging a word line to a reference
voltage, wherein the word line is connected to a memory cell,
wherein the memory cell comprises at least two p-type pass gates
which connect the memory cell correspondingly to a bit line and a
bit line bar; activating a voltage control unit connected to the
word line by a series connection of a p-type capacitor-connected
transistor and a first inverter, the first inverter having an input
terminal configured to receive a data signal and an output terminal
connected to the word line, the first inverter being connected
between a supply voltage and a first node; wherein the activating
the voltage control unit comprises: outputting a first control
signal from a second inverter included in the voltage control unit
to a voltage adjuster, the voltage adjuster including an n-type
transistor connected between a ground voltage and the first node;
and controlling the voltage adjuster in response to the first
control signal, the controlling the voltage adjuster including:
selectively adjusting a first data signal on the bit line connected
to the memory cell; selectively adjusting a second data signal on
the bit line bar connected to the memory cell; and affecting
operation of the first inverter and which thereby causes a voltage
on the word line to undergo at least a double transition including
a first transition to the ground voltage and then a second
transition to an intermediate voltage which is greater than the
ground voltage but substantially lower than the supply voltage.
16. The method of claim 15, wherein: after the voltage on the word
line undergoes the second transition from the ground voltage to the
intermediate voltage, the controlling the voltage adjuster further
causes the voltage on the word line to undergo a third transition
from the intermediate voltage to the ground voltage.
17. The method of claim 15, wherein: the voltage control unit
further includes: series-connected inverters coupled between the
p-type capacitor-connected transistor and a timing control unit,
the series-connected inverters including the second inverter; and
the activating a voltage control unit includes: receiving a second
control signal from the timing control unit; and using the
series-connected inverters to provide a delayed version of the
second control signal as the first control signal.
18. The method of claim 15, wherein: the voltage control unit
further includes: series-connected inverters coupled between the
p-type capacitor-connected transistor and a timing control unit,
the series-connected inverters including the second inverter; and
the controlling the voltage adjuster further includes: using the
series-connected inverters to provide a delayed version of the
control signal to a gate electrode of the N-type transistor as the
first control signal.
19. The method of claim 18, wherein the using the series-connected
inverters to provide a delayed version of the control signal to a
gate electrode of the N-type transistor includes: using a signal on
a second node between first and second ones of the series-connected
inverters as the delayed version of the control signal.
20. The method of claim 15, wherein: the memory cell is a
single-port memory cell, a two-port memory cell or a dual-port
memory cell.
Description
BACKGROUND
The semiconductor integrated circuit (IC) industry has produced a
wide variety of digital devices to address issues in a number of
different areas. Some of these digital devices are electrically
coupled to static random access memory (SRAM) devices for the
storage of digital data. As ICs have become smaller and more
complex, operating voltages continue to decrease affecting IC
performance.
BRIEF DESCRIPTION OF THE DRAWINGS
Aspects of the present disclosure are best understood from the
following detailed description when read with the accompanying
figures. It is noted that, in accordance with the standard practice
in the industry, various features are not drawn to scale. In fact,
the dimensions of the various features may be arbitrarily increased
or reduced for clarity of discussion.
FIG. 1 is block diagram of a representative portion of a memory
cell array in accordance with some embodiments.
FIG. 2A is schematic diagram of a write logic cell in accordance
with some embodiments.
FIG. 2B is schematic diagram of a write logic cell in accordance
with some embodiments.
FIG. 3A is a schematic diagram of memory cell in accordance with
some embodiments.
FIG. 3B is a schematic diagram of memory cell in accordance with
some embodiments.
FIG. 3C is a schematic diagram of memory cell in accordance with
some embodiments.
FIG. 4 is a waveform diagram of signals applied to a write logic
cell of an SRAM in accordance with some embodiments.
FIG. 5 is schematic diagram of a write logic cell in accordance
with some embodiments.
FIG. 6A is schematic diagram of a voltage control unit in
accordance with some embodiments.
FIG. 6B is schematic diagram of a voltage control unit in
accordance with some embodiments.
FIG. 7A is a waveform diagram of signals applied to a write logic
cell of an SRAM for a write operation in accordance with one or
more embodiments.
FIG. 7B is a waveform diagram of signals applied to a write logic
cell of an SRAM for a write operation in accordance with one or
more embodiments.
FIG. 8A is schematic diagram of a logic cell in accordance with
some embodiments.
FIG. 8B is schematic diagram of a logic cell in accordance with
some embodiments.
FIG. 9 is a waveform diagram of signals applied to one or more
write logic cells of an SRAM in accordance with some
embodiments.
FIG. 10 is schematic diagram of a write logic cell in accordance
with some embodiments.
FIG. 11A is schematic diagram of a voltage control unit in
accordance with some embodiments.
FIG. 11B is schematic diagram of a voltage control unit in
accordance with some embodiments.
FIG. 11C is schematic diagram of a voltage control unit in
accordance with some embodiments.
FIG. 12A is a waveform diagram of signals applied to a write logic
cell of an SRAM for a write operation in accordance with some
embodiments.
FIG. 12B is a waveform diagram of signals applied to a write logic
cell of an SRAM for a write operation in accordance with some
embodiments.
FIG. 12C is a waveform diagram of signals applied to a write logic
cell of an SRAM for a write operation in accordance with some
embodiments.
FIG. 13A is schematic diagram of a read logic cell in accordance
with some embodiments.
FIG. 13B is schematic diagram of a read logic cell in accordance
with some embodiments.
FIG. 14A is a waveform diagram of signals applied to a read logic
cell of an SRAM when the voltage control unit is not operational in
accordance with some embodiments.
FIG. 14B is a waveform diagram of signals applied to a read logic
cell of an SRAM in accordance with one or more embodiments.
FIG. 15 is a flow chart of a method of controlling an SRAM in
accordance with some embodiments.
DETAILED DESCRIPTION
The following disclosure provides many different embodiments, or
examples, for implementing different features of the provided
subject matter. Specific examples of components and arrangements
are described below to simplify the present disclosure. These are,
of course, merely examples and are not intended to be limiting. For
example, the formation of a first feature over or on a second
feature in the description that follows may include embodiments in
which the first and second features are formed in direct contact,
and may also include embodiments in which additional features may
be formed between the first and second features, such that the
first and second features may not be in direct contact. In
addition, the present disclosure may repeat reference numerals
and/or letters in the various examples. This repetition is for the
purpose of simplicity and clarity and does not in itself dictate a
relationship between the various embodiments and/or configurations
discussed.
Further, spatially relative terms, such as "beneath," "below,"
"lower," "above," "upper" and the like, may be used herein for ease
of description to describe one element or feature's relationship to
another element(s) or feature(s) as illustrated in the figures. The
spatially relative terms are intended to encompass different
orientations of the device in use or operation in addition to the
orientation depicted in the figures. The apparatus may be otherwise
oriented (rotated 90 degrees or at other orientations) and the
spatially relative descriptors used herein may likewise be
interpreted accordingly.
FIG. 1 is a block diagram of a representative portion of a memory
cell array 100 in accordance with one or more embodiments. Memory
cell array 100 comprises an array of memory cells including M rows
by N columns, where M is an integer corresponding to the number of
rows and N is an integer corresponding to the number of columns. In
some embodiments, M is an integer ranging from 1 to 256. In some
embodiments, N is an integer ranging from 1 to 256.
In some embodiments, memory cell array 100 comprises one or more
single port (SP) static random access memory (SRAM) cells. In some
embodiments, memory cell array 100 comprises one or more dual port
(DP) SRAM cells. In some embodiments, memory cell array 100
comprises one or more two port (2P) SRAM cells. In some
embodiments, write ports are used. In some embodiments, read ports
are used. In some embodiments, additional write ports and/or read
ports are used. In some embodiments, memory cell array 100 includes
a single write port or read port. In some embodiments, memory cell
array 100 includes more than one write port or read port.
M write word line (WWL) terminals (WWL[0]-WWL[M-1]) carry signals
to activate corresponding rows in the memory cell array 100. WWL[0]
terminal 102 is electrically connected to WWL terminals of memory
cells 104, 106, 108, 110, 112 that form row 0 of the memory cell
array 100. WWL[1] terminal 114 is electrically connected to WWL
terminals of memory cells 116, 118, 120, 122, 124 that form row 1
of the memory cell array 100. WWL[2] terminal 126 is electrically
connected to WWL terminals of memory cells 128, 130, 132, 134, 136
that form row 2 of the memory cell array 100. WWL[M-1] terminal 138
is electrically connected to WWL terminals of memory cells 140,
142, 144, 146, 148 that form row M-1 of the memory cell array
100.
N write bit line (WBL) terminals (WBL[0]-WBL[N-1]) and N write bit
line bar (WBLB) terminals (WBLB[0]-WBLB[N-1]) carry data signals
for storage in selected memory cells in a column in the memory cell
array 100. WBL[0] terminal 150 and WBLB[0] terminal 152 are
electrically connected to the corresponding WBL and WBLB terminals
of memory cells 104, 116, 128, 140 that form column 0 of memory
cell array 100. WBL[1] terminal 154 and WBLB[1] terminal 156 are
electrically connected to the corresponding WBL and WBLB terminals
of memory cells 106, 118, 130, 142 that form column 1 of memory
cell array 100. WBL[2] terminal 158 and WBLB[2] terminal 160 are
electrically connected to the corresponding WBL and WBLB terminals
of memory cells 108, 120, 132, 144 that form column 2 of memory
cell array 100. WBL[3] terminal 162 and WBLB[3] terminal 164 are
electrically connected to the corresponding WBL and WBLB terminals
of memory cells 110, 122, 134, 146 that form column 3 of memory
cell array 100. WBL[N-1] terminal 166 and WBLB[N-1] terminal 168
are electrically connected to the corresponding WBL and WBLB
terminals of memory cells 112, 124, 136, 148 that form column N-1
of memory cell array 100.
N read bit line (RBL) terminals (RBL[0]-RBL[N-1]) carry data
signals in selected cells in a column in the memory cell array 100.
RBL[0] terminal 170 is electrically connected to the RBL terminals
of memory cells 104, 116, 128, 140 that form column 0 of memory
cell array 100. RBL[1] terminal 172 is electrically connected to
the RBL terminals of memory cells 106, 118, 130, 142 that form
column 1 of memory cell array 100. RBL[2] terminal 174 is
electrically connected to the RBL terminals of memory cells 108,
120, 132, 144 that form column 2 of memory cell array 100. RBL[3]
terminal 176 is electrically connected to the RBL terminals of
memory cells 110, 122, 134, 146 that form column 3 of memory cell
array 100. RBL[N-1] terminal 178 is electrically connected to the
RBL terminals of memory cells 112, 124, 136, 148 that form column
N-1 of memory cell array 100.
M read word line (RWL) terminals (RWL[0]-RWL[M-1]) are used to
activate a row of memory cells in the memory cell array 100. RWL[0]
terminal 180 is electrically connected to the RWL terminals of row
0 of memory cell array 100. RWL[1] terminal 182 is electrically
connected to the RWL terminals of row 1 of memory cell array 100.
RWL[2] terminal 184 is electrically connected to the RWL terminals
of row 2 of memory cell array 100. RWL[M-1] terminal 186 is
electrically connected to the RWL terminals of row M-1 of memory
cell array 100.
FIG. 2A is a schematic diagram of a write logic cell 200 in
accordance with one or more embodiments. Memory cell 204 is an
embodiment of memory cell 104 shown in FIG. 1. Word line WL 206 is
an embodiment of write word line WWL[0] 102 shown in FIG. 1. Bit
line BL 208 is an embodiment of write bit line WBL[0] 150 shown in
FIG. 1. Bit line bar BLB 210 is an embodiment of write bit line bar
WBLB[0] 152 shown in FIG. 1.
Write logic cell 200 comprises memory cell 204 and bit line control
unit 202. Memory cell 204 is connected to bit line control unit 202
by bit line BL 208 and bitline bar BLB 210. In some embodiments,
one bit line control unit 202 is connected to one or more memory
cells. In some embodiments, one or more bit line control units 202
are connected to at least one memory cell.
Bit line control unit 202 is configured to receive a clock signal
CLKW, a tracking control signal TM_BBL, a select control signal
BBL_TSEL, a data signal DATA and a multiplexer signal Yb_write[0].
Bit line control unit 202 is configured to send signal BL/BLB to
memory cell 204 by the bit line BL 208 and bit line bar BLB 210.
Bit line control unit 202 comprises a timing unit 212, a voltage
control unit 214, a first write driver 216, a second write driver
218, a Y-Multiplexer 220, inverter I5, inverter I6, PMOS transistor
P1, PMOS transistor P2 and PMOS transistor P3.
Timing unit 212 is configured to receive clock signal CLKW,
tracking control signal TM_BBL and select control signal BBL_TSEL.
The clock signal CLKW is, e.g., a logically low signal or a
logically high signal. The tracking control signal TM_BBL is, e.g.,
a logically low signal or a logically high signal. In some
embodiments, the select control signal BBL_TSEL is, e.g., a
logically low signal or a logically high signal. In some
embodiments, select control signal BBL_TSEL is a multiple bit
signal with more than two logical states.
Timing unit 212 is configured to send a control signal to voltage
control unit 214. In some embodiments, the control signal sent to
the voltage control unit 214 is an embodiment of the first voltage
control signal header_enb prior to the inverters I1 and I2. The
first voltage control signal header_enb is, e.g., a logically low
signal or a logically high signal. In some embodiments, timing unit
212 is configured to control the timing of the bit line control
unit 202. In some embodiments, timing unit 212 is configured to
control the pulse width of the first voltage control signal
header_enb. In some embodiments, timing unit 212 is configured to
control the rising edge or the falling edge of the first voltage
control signal header_enb. Timing unit 212 is connected to voltage
control unit 214. Timing unit 212 includes three inputs; one input
of timing unit 212 is connected to the source of the clock signal
CLKW, one input of timing unit 212 is connected to the source of
the tracking control signal TM_BBL, and one input of timing unit
212 is connected to the source of the select control signal
BBL_TSEL.
Voltage control unit 214 comprises inverter I1, inverter I2,
inverter I3, inverter I4 and NMOS transistor N1. Voltage control
unit 214 is configured to receive a signal from timing unit 212.
Voltage control unit 214 is configured to send first voltage
control signal header_enb to PMOS transistor P1. Voltage control
unit 214 is configured to control a boosted voltage signal BVDD. In
some embodiments, the boosted voltage signal BVDD ranges from about
a first high signal level HIGH1 to about a second high signal level
HIGH2. In some embodiments, first high signal level HIGH1 is
substantially equal to VDD. In some embodiments, second high signal
level HIGH2 is substantially equal to VDD+.DELTA.Vbvdd volts, where
.DELTA.Vbvdd is a first boosted voltage level. In some embodiments,
the first boosted voltage level .DELTA.Vbvdd ranges from about 0
volts to about 200 millivolts (mV). In some embodiments, a voltage
control unit 214 is one or more voltage controllers. In some
embodiments, a voltage controller is configured to selectively
adjust the voltage of the memory cell.
Inverter I1 is connected to timing unit 212 and inverter I2.
Inverter I1 is configured to receive a control signal from the
timing unit 212. Inverter I1 is configured to send an inverted
version of the control signal to inverter I2.
Inverter I2 is connected to inverter I1, inverter I3 and PMOS
transistor P1. Inverter I2 is configured to receive the inverted
version of the control signal from inverter I1. Inverter I2 is
configured to send a first voltage control signal header_enb to
inverter I3 and PMOS transistor P1.
Inverter I3 is connected to inverter I2, inverter I4 and PMOS
transistor P1. Inverter I3 is configured to receive the first
voltage control signal header_enb from inverter I3. Inverter I3 is
configured to send an inverted version of the first voltage control
signal header_enb to inverter I4.
Inverter I4 is connected to inverter I3 and NMOS transistor N1.
Inverter I4 is configured to receive the inverted version of the
first voltage control signal header_enb from inverter I3. Inverter
I4 is configured to send a second voltage control signal BBL_en to
NMOS transistor N1. In some embodiments, the second voltage control
signal BBL_en is a delayed version of the first voltage control
signal header_enb. The second voltage control signal BBL_en is,
e.g., a logically low signal or a logically high signal.
The drain of NMOS transistor N1 is connected to the source of NMOS
transistor N1. The gate of NMOS transistor N1 is connected to the
drain of PMOS transistor P1, first write driver 216, second write
driver 218 and Y-Multiplexer 220. In some embodiments, NMOS
transistor N1 functions as a capacitor, since the drain and source
terminals of the NMOS transistor N1 are coupled together. In some
embodiments, NMOS transistor N1 is configured to control the
boosted voltage signal BVDD. In some embodiments, the second
voltage control signal BBL_en controls the charging/discharging of
the NMOS transistor N1.
The gate of PMOS transistor P1 is connected to inverter I2 and
inverter I3. The gate of PMOS transistor P1 is configured to
receive the first voltage control signal header_enb. The source of
PMOS transistor P1 is connected to voltage source VDD. The drain of
PMOS transistor P1 is connected to the gate of NMOS transistor N1,
first write driver 216, second write driver 218 and Y-Multiplexer
220. In some embodiments, the first voltage control signal
header_enb selectively turns on/off PMOS transistor P1. In some
embodiments, PMOS transistor P1 is configured to control the
boosted voltage signal BVDD. In some embodiments, the first voltage
control signal header_enb and the second voltage control signal
BBL_en controls the charging/discharging of the NMOS transistor
N1.
Inverter I5 is connected to inverter I6. Inverter I5 is configured
to receive a data signal DATA. In some embodiments, the data signal
DATA is, e.g., a logically low signal or a logically high signal.
Inverter I5 is configured to send an inverted version of the data
signal DATA to inverter I6 and first write driver 216.
First write driver 216 comprises inverter I8. Inverter I8 is
connected to inverter I5, inverter I6, second write driver 218,
Y-Multiplexer 220, PMOS transistor P1, PMOS transistor P2 and NMOS
transistor N1. Inverter I8 is configured to receive an inverted
version of the data signal DATA. Inverter I8 is configured to
receive the boosted voltage signal BVDD. In some embodiments,
inverter I8 is configured such that the boosted voltage signal BVDD
is connected to the operating voltage terminal of the inverter I8.
Inverter I8 is configured to send a data signal Din to PMOS
transistor P2 by the bit line BL 208. In some embodiments, the data
signal Din is, e.g., a logically low signal or a logically high
signal. In some embodiments, the data signal Din is substantially
equal to a bit line voltage signal BL. In some embodiments, the bit
line voltage signal BL or bit line bar voltage signal BLB is a
value ranging from a logically low level to about a second high
signal level HIGH2'. In some embodiments, the second high signal
level HIGH2' is substantially equal to VDD+.DELTA.Vb1 volts, where
.DELTA.Vb1 is a second boosted voltage level. In some embodiments,
the second boosted voltage level .DELTA.Vb1 ranges from about 0
volts to about 150 mV. In some embodiments, the second boosted
voltage level .DELTA.Vb1 is less than the first boosted voltage
level .DELTA.Vbvdd.
Inverter I6 is connected to inverter I5, first write driver 216 and
second write line driver 218. Inverter I6 is configured to receive
an inverted version of the data signal DATA. Inverter I6 is
configured to send a delayed version of the data signal DATA to the
second write driver 218.
Second write driver 218 comprises inverter I7. Inverter I7 is
connected to inverter I6, first write driver 216, Y-Multiplexer
220, PMOS transistor P1, PMOS transistor P3 and NMOS transistor N1.
Inverter I7 is configured to receive the delayed version of the
data signal DATA. Inverter I7 is configured to receive the boosted
voltage signal BVDD. In some embodiments, inverter I7 is configured
such that the boosted voltage signal BVDD is connected to the
operating voltage terminal of the inverter I7. Inverter I7 is
configured to send an inverted data signal Dinb to PMOS transistor
P3 by the bit line bar BLB 210. In some embodiments, the inverted
data signal Dinb is, e.g., a logically low signal or a logically
high signal. In some embodiments, the inverted data signal Dinb is
substantially equal to a bit line bar voltage signal BLB.
Y-Multiplexer 220 is connected to first write driver 216, second
write driver 218, PMOS transistor P1, PMOS transistor P2, PMOS
transistor P3 and NMOS transistor N1. Y-Multiplexer 220 is
configured to receive a signal Yb_write[0]. Y-Multiplexer 220 is
configured to receive boosted voltage signal BVDD. Y-Multiplexer
220 is configured to send a control signal to the gates of PMOS
transistors P2 and P3. Y-Multiplexer 220 comprises inverter I9 and
inverter I10.
Inverter I9 is connected to inverter I10. Inverter I9 is configured
to receive a signal Yb_write[0]. In some embodiments, the signal
Yb_write[0] is, e.g., a logically low signal or a logically high
signal. Inverter I9 is configured to send an inverted version of
the signal Yb_write[0] to inverter I10.
Inverter I10 is connected to inverter I9, first write driver 216,
second write driver 218, PMOS transistor P1, PMOS transistor P2,
PMOS transistor P3 and NMOS transistor N1. Inverter I10 is
configured to receive an inverted version of signal Yb_write[0] and
boosted voltage signal BVDD. In some embodiments, inverter I10 is
configured such that the boosted voltage signal BVDD is connected
to the operating voltage terminal of the inverter I10. Inverter I10
is configured to send a control signal to the gates of PMOS
transistors P2 and P3.
The gate of PMOS transistor P2 is connected to the Y-Multiplexer
220. The gate of PMOS transistor P2 is configured to receive the
control signal from the Y-Multiplexer 220. The source of PMOS
transistor P2 is connected to memory cell 204 by the bit line BL
208. The drain of PMOS transistor P2 is connected to the first
write driver 216. The drain of PMOS transistor P2 is configured to
receive data signal Din.
The gate of PMOS transistor P3 is connected to the Y-Multiplexer
220. The gate of PMOS transistor P3 is configured to receive the
control signal from the Y-Multiplexer 220. The source of PMOS
transistor P3 is connected to memory cell 204 by the bit line bar
BLB 210. The drain of PMOS transistor P3 is connected to the second
write driver 218. The drain of PMOS transistor P3 is configured to
receive inverted data signal Dinb.
FIG. 2B is a schematic diagram of a write logic cell 200 in
accordance with one or more embodiments. Write logic cell 200' is
an embodiment of write logic cell 200 shown in FIG. 2A with similar
elements. Bit line control unit 202' is an embodiment of bit line
control unit 202' shown in FIG. 2A with similar elements. In
comparison with FIG. 2A, FIG. 2B comprises timing unit 212' instead
of timing unit 212, and voltage control unit 214' instead of
voltage control unit 214'. Timing unit 212' is an embodiment of
timing unit 212 shown in FIG. 2A. Voltage control unit 214' is an
embodiment of voltage control unit 214 shown in FIG. 2A.
Timing unit 212' is configured to receive clock signal CLKW,
tracking control signal TM_BBL and select control signal BBL_TSEL.
Timing unit 212' is configured to send a control signal to voltage
control unit 214'. In some embodiments, timing unit 212' is
configured to control the timing of the bit line control unit 202'.
Timing unit 212' is connected to voltage control unit 214'. Timing
unit 212' includes three inputs; one input of timing unit 212' is
connected to the source of the clock signal CLKW, one input of
timing unit 212' is connected to the source of the tracking control
signal TM_BBL and one input of timing unit 212' is connected to the
source of the select control signal BBL_TSEL.
Voltage control unit 214' is configured to receive a signal from
timing unit 212'. Voltage control unit 214' is configured to
control a boosted voltage signal BVDD. In some embodiments, a
voltage control unit 214' is one or more voltage controllers. In
some embodiments, a voltage controller is configured to selectively
adjust the voltage of the memory cell.
The gate of PMOS transistor P1 is configured to receive the first
voltage control signal header_enb. The gate of PMOS transistor P1
is connected the source of the first voltage control signal
header_enb.
The source of PMOS transistor P1 is connected to voltage source
VDD. The drain of PMOS transistor P1 is connected to the voltage
control unit 214', first write driver 216, second write driver 218
and Y-Multiplexer 220. In some embodiments, the first voltage
control signal header_enb selectively turns on/off PMOS transistor
P1. In some embodiments, PMOS transistor P1 is configured to
control the boosted voltage signal BVDD. In some embodiments, the
first voltage control signal header_enb and the second voltage
control signal BBL_en controls the charging/discharging of the NMOS
transistor N1.
FIG. 3A is a schematic diagram of a memory cell 300a in accordance
with one or more embodiments. Memory cell 300a is an embodiment of
one or more memory cells shown in FIG. 1. In some embodiments, the
memory cell 300a is a six transistor (6T) single port (SP) SRAM
memory cell. In some embodiments, the memory cell 300a employs a
number of transistors other than six. The memory cell 300a
comprises a pair of cross-coupled inverters 302, first pass gate
312 and second pass gate 314.
The cross-coupled inverters 302 include two p-type metal oxide
semiconductor (PMOS) transistors 304, 306 each having source
terminals electrically connected to a power supply voltage (VDD)
terminal. The two PMOS transistors 304, 306 each have drain
terminals separately electrically connected to drain terminals of
two n-type metal oxide semiconductor (NMOS) transistors 308, 310 at
corresponding nodes T and C. Source terminals of NMOS transistors
308, 310 are electrically connected to node CV. In some
embodiments, node CV is substantially equal to a logically low
signal. In some embodiments, node CV is substantially equal to a
ground voltage (VSS). A gate terminal of PMOS transistor 304 is
electrically connected to a gate terminal of NMOS transistor 308
and the drain terminal of NMOS transistor 310. Similarly, a gate
terminal of PMOS transistor 306 is electrically connected to a gate
terminal of NMOS transistor 310 and the drain terminal of NMOS
transistor 308.
First pass gate 312 is configured to selectively connect
cross-coupled inverters 302 to a bit line BL 318. Second pass gate
314 is configured to selectively connect cross-coupled inverters
302 to a bit line bar BLB 320. First pass gate 312 and second pass
gate 314 are both configured to be activated based on a signal
supplied by a word line WL 316. In some embodiments, first pass
gate 312 or second pass gate 314 is a PMOS transistor. In some
embodiments, first pass gate 312 or second pass gate 314 include
three-dimensional gate structures, e.g. fin
field-effect-transistors (FinFET). Note that the term "bar" as used
in this context indicates a logically inverted signal, for example,
bit line bar BLB 320 carries a signal logically inverted from a
signal carried by bit line BL 318.
In contrast with memory cells which include n-type transistors for
pass gates, memory cell array 300a is connected to the bit line BL
318 and bit line bar BLB 320 by a logically low signal at a gate of
first pass gate 312 and second pass gate 314.
As semiconductor devices are scaled down, a driving strength of a
p-type transistor increases in comparison with a driving strength
of an n-type transistor. The result is that higher currents are
able to be conveyed through p-type transistors in scaled down
semiconductor devices. By using p-type transistors for first pass
gate 312 and second pass gate 314 for scaled down semiconductor
devices, bit information stored in cross-coupled inverters 302 is
conveyed to bit line BL 318 or bit line bar BLB 320 more rapidly in
comparison with scaled down semiconductor devices which include
n-type transistors for pass gates.
FIG. 3B is a schematic diagram of a memory cell 300b in accordance
with one or more embodiments. Memory cell 300b is an embodiment of
memory cell 300a (shown in FIG. 3a) with similar elements. In some
embodiments, the memory cell 300b is an eight transistor (8T) dual
port (DP) SRAM memory cell. In some embodiments, the memory cell
300b employs a number of transistors other than eight. The memory
cell 300b comprises a pair of cross-coupled inverters 302, first
pass gate 312, second pass gate 314, third pass gate 322 and fourth
pass gate 324.
First pass gate 312 is configured to selectively connect
cross-coupled inverters 302 to a first bit line A_BL 318a. Second
pass gate 314 is configured to selectively connect cross-coupled
inverters 302 to a first bit line bar A_BLB 320a. Third pass gate
322 is configured to selectively connect cross-coupled inverters
302 to a second bit line B_BL 318b. Fourth pass gate 326 is
configured to selectively connect cross-coupled inverters 302 to a
second bit line bar B_BLB 326. Both first pass gate 312 and second
pass gate 314 are configured to be activated based on a signal
supplied by a first word line A_WL 316a. Third pass gate 322 and
fourth pass gate 324 are both configured to be activated based on a
signal supplied by a second word line B_WL 328. In some
embodiments, first pass gate 312 or second pass gate 314 is a PMOS
transistor. In some embodiments, third pass gate 322 or fourth pass
gate 324 is a PMOS transistor. In some embodiments, one or more of
first pass gate 312, second pass gate 314 third pass gate 322 or
fourth pass gate 324 include three-dimensional gate structures,
e.g. FinFETs.
In contrast with memory cells which include n-type transistors for
pass gates, memory cell array 300b is connected to the first bit
line A_BL 318a, second bit line B_BL 318b, first bit line bar A_BLB
320a or fourth bit line bar B_BLB 326 by a logically low signal at
a gate of first pass gate 312, second pass gate 314, third pass
gate 322 or fourth pass gate 324.
FIG. 3C is a schematic diagram of a memory cell 300c in accordance
with one or more embodiments. Memory cell 300c is an embodiment of
memory cell 300a (shown in FIG. 3a) with similar elements. In some
embodiments, the memory cell 300c is an eight transistor (8T) two
port (2P) SRAM memory cell. In some embodiments, the memory cell
300c employs a number of transistors other than eight. In
comparison with the memory cell 300a (shown in FIG. 3a), memory
cell 300c also includes a read port transistor 322a and a read bit
line transistor 324a. Write word line WWL 316' is an embodiment of
word line 316 shown in FIG. 3a. Write bit line WBL 318' is an
embodiment of bit line 318 shown in FIG. 3a. Write bit line bar
WBLB 320' is an embodiment of bit line bar 320 shown in FIG.
3a.
Read port transistor 322a is connected to read bit line transistor
324a. In some embodiments, read port transistor 322a and read bit
line transistor 324a facilitate a read operation and a write
operation to be performed on memory cell 300c during a same cycle.
Read port transistor 322a is a p-type transistor. In some
embodiments, read port transistor 322a includes a three-dimensional
gate structure, e.g., FinFET. A gate of read port transistor 322a
is connected to second pass gate 314 and the cross-coupled
inverters 302 (by node C). A source of read port transistor 322a is
connected to voltage source VDD. A drain of read port transistor
322a is connected to read bit line transistor 324a.
Read port transistor 322a is configured to selectively connect the
voltage source VDD to read bit line transistor 324a based on a
voltage level at node C of the cross-coupled inverters 302. In
operation, when a logically high value is at node C of the
cross-coupled inverters 302, read port transistor 322a is
non-conductive, and read bit line transistor 324a is floating. When
a logically low value is at node C of the cross-coupled inverters
302, read port transistor 322a is conductive and read bit line
transistor 324a is connected to the voltage source VDD.
Read bit line transistor 324a is a p-type transistor. In some
embodiments, read bit line transistor 324a includes a
three-dimensional gate structure, e.g., FinFET. A gate of read bit
line transistor 324a is configured to receive a signal from a read
word line RWL 328'. A source of read bit line transistor 324a is
connected to read port transistor 322a. A drain of read bit line
transistor 324a is connected to read bit line RBL 326'.
Read bit line transistor 324a is configured to selectively connect
the read bit line RBL 326' to read port transistor 322a. In
operation, when a signal on read write line RWL 328' activates read
bit line transistor 324a and the read bit line transistor 324a is
floating (by read port transistor 322a), a voltage level on read
bit line RBL 326' remains unchanged. When a signal on read write
line RWL activates read bit line transistor 324a and the read bit
line transistor 324a is connected to the voltage source VDD (by
read port transistor 322a), a voltage level on read bit line RBL
326' is pulled up to the operating voltage (e.g., voltage source
VDD or a logically high signal). A voltage level on read bit line
RBL 326' is usable to determine bit information stored in
cross-coupled inverters 302.
FIG. 4 is a waveform diagram of signals applied to a write logic
cell 200 of an SRAM in accordance with one or more embodiments.
Curve 402 represents the signal on the word line WL (e.g., word
line WL 316 shown in FIG. 3A, first word line A_WL 316a or second
word line A_WL 328 shown in FIG. 3B and write word line WWL 316'
shown in FIG. 3C); curve 404 represents the first voltage control
signal header_enb; curve 406 represents the second voltage control
signal BBL_en; curve 408 represents the boosted voltage signal
BVDD; curves 410a, 410b represent the bit line/bit line bar signal
BL/BLB; and curves 412a, 412b represent the signal on data nodes
C/T of cross-coupled inverters 302. FIG. 4 shows waveforms of
various signals when memory cell 204 is accessed for a write
operation.
At time T1, curve 402 (e.g., word line signal WL) transitions from
a logically high signal to a logically low signal. At time T1,
curve 410b (e.g., bit line/bit line bar BL/BLB) transitions from a
logically low signal to a first high signal level HIGH1'. In some
embodiments, when curve 402 transitions to a logically low signal,
the first pass gate 312 and the second pass gate 314 (as shown in
FIG. 3A-3C) each turn-on connecting the bit line BL/bit line bar
BLB to the cross-coupled inverters 302.
At time T2, curve 404 (e.g., first voltage control signal
header_enb) starts transitioning from a logically low signal to a
logically high signal.
At time T3, curve 404 (e.g., first voltage control signal
header_enb) finishes transitioning from a logically low signal to a
logically high signal. In some embodiments, when curve 404
transitions to a logically high signal, the PMOS transistor P1 (as
shown in FIGS. 2A-2B) turns-off which disconnects the gate of the
NMOS transistor N1 from the voltage source VDD.
At time T4, curve 406 (e.g., second voltage control signal BBL_en)
transitions from a logically low signal to a logically high signal.
At time T4, curve 408 (e.g., boosted voltage signal BVDD)
transitions from a first high signal level HIGH1 to a second high
signal level HIGH2. At time T4, curve 410a (e.g., bit line/bit line
bar signal BL/BLB) transitions from a first high signal level
HIGH1' to a second high signal level HIGH2'. At time T4, curve 412a
transitions from an intermediate signal level to a logically high
signal level and curve 412b transitions from an intermediate signal
level to a logically low signal level. In some embodiments, the
curves 412a, 412b represent the ability of cross-coupled inverters
302 to transition from a low logical state to a high logical state
and vice versa for the storage of a unit of data in a memory cell
204.
In some embodiments, the first high signal level HIGH1 is
substantially equal to voltage source VDD. In some embodiments, the
second high signal level HIGH2 is substantially equal to
VDD+.DELTA.Vbvdd, where .DELTA.Vbvdd is a first boosted voltage
level. In some embodiments, the first signal level HIGH1' is
substantially equal to voltage source VDD. In some embodiments, the
second signal level HIGH2' is substantially equal to
VDD+.DELTA.Vb1, where .DELTA.Vb1 is a second boosted voltage level.
In some embodiments, NMOS transistor N1 functions as a capacitor
since the source and drain are coupled together.
In some embodiments, a change in the first voltage control signal
header_enb (e.g., curve 404) and the second voltage control signal
BBL_en (e.g., curve 406), causes the NMOS transistor N1 to
discharge resulting in a change in the boosted voltage signal BVDD
(e.g., curve 408). In some embodiments, the change in the first
voltage control signal header_enb (e.g., curve 404) directly
results in a change in the second voltage control signal BBL_en
(e.g., curve 406). In some embodiments, the change in the first
voltage control signal header_enb (e.g., curve 404) or the second
voltage control signal BBL_en (e.g., curve 406), triggers a
corresponding change in both the boosted voltage signal BVDD (e.g.,
curve 408) and the bit line/bit line bar signal BL/BLB (e.g., curve
410a). In some embodiments, a change in the boosted voltage signal
BVDD (e.g., curve 408) results in a corresponding change of the bit
line/bit line bar signal BL/BLB (e.g., curve 410a).
At time T5, curve 408 (e.g., boosted voltage signal BVDD) finishes
transitioning to a second high signal level HIGH2. At time T5,
curve 410a (e.g., bit line/bit line bar signal BL/BLB) finishes
transitioning to a second high signal level HIGH2'.
At time T6, curve 404 (e.g., first voltage control signal
header_enb) transitions from a logically high signal to a logically
low signal.
At time T7, curve 402 begins transitioning to a logically high
signal.
At time T8, curve 402 finishes transitioning to a logically high
signal. In some embodiments, when curve 402 transitions to a
logically high signal, the first pass gate 312 and the second pass
gate 314 (as shown in FIG. 3A-3C) each turn-off and disconnect the
bit line BL/bit line bar BLB from the cross-coupled inverters 302.
In some embodiments, a single write cycle of the word line is
represented by curve 402. At time T8, curve 406 (e.g. second
voltage control signal BBL_en) transitions from a logically high
signal to a logically low signal. At time T8, curve 408 (e.g.
Boosted voltage signal BVDD) transitions from a second high signal
level HIGH2 to a first high signal level HIGH1. At time T8, curve
410a (e.g., bit line/bit line bar signal BL/BLB) transitions from a
second high signal level HIGH2' to a logically low signal (e.g.,
curve 410b).
At time T9, curve 406 (e.g., second voltage control signal BBL_en)
and curve 408 (e.g., boosted voltage signal BVDD) finish
transitioning to a logically low signal.
In some embodiments, curves 410a, 410b (e.g., bit line signal BL
and bit line bar signal BLB) transition to a voltage level greater
than voltage source VDD which strengthens the capability of the
first pass gate 312, the second pass gate 314, third pass gate 322
and fourth pass gate 324 (as shown in FIGS. 3A-3C). In some
embodiments, when curves 410a, 410b (e.g., bit line signal BL and
bit line bar signal BLB) transition to a voltage level greater than
voltage source VDD, the operating region (e.g., VCCmin) of memory
cell 204 is improved. In some embodiments, the operating region
(e.g., VCCmin) of memory cell 204 is the minimum voltage at which
the memory cell can reliably operate. In some embodiments, by
controlling the pulse width of the first voltage control signal
header_enb, the pulse width of the boosted voltage signal BVDD is
controlled. In some embodiments, by controlling the pulse width of
the first voltage control signal header_enb, the length of time the
bit line signal BL or bit line bar signal BLB is raised or lifted
up to the second high signal HIGH2' is controlled.
FIG. 5 is a schematic diagram of a write logic cell 500 in
accordance with one or more embodiments. Memory cell 204 is an
embodiment of memory cell 104 shown in FIG. 1. Memory cell 540 is
an embodiment of memory cell 140 shown in FIG. 1. Word line WL[0]
206 is an embodiment of write word line WWL[0] 102 shown in FIG. 1.
Word line WL[M-1] 508 is an embodiment of write word line WWL[M-1]
138 shown in FIG. 1. Bit line BL 208 is an embodiment of write bit
line WBL[0] 150 shown in FIG. 1. Bit line bar BLB 210 is an
embodiment of write bit line bar WBLB[0] 152 shown in FIG. 1.
Write logic cell 500 comprises a voltage control unit 502 connected
to memory cell 204 and memory cell 540. Memory cell 204 and memory
cell 540 are connected to voltage control unit 502 by CV line 504
at node CV. Memory cell 204 and memory cell 540 are connected to
each other by bit line BL 208 and bit line bar BLB 210. In some
embodiments, voltage control unit 502 is connected to one or more
memory cells in memory cell array 100. In some embodiments, a
plurality of voltage control units 502 are each connected to one or
more memory cells in memory cell array 100. In some embodiments, CV
line 504 is a data line connected to VSS.
Voltage control unit 502 is configured to receive a first voltage
signal RGV_ENB. Voltage control unit 502 is configured to control a
second voltage signal CVSS on CV line 504. Voltage control unit 502
comprises an NMOS transistor N2 and a PMOS transistor P4. In some
embodiments, voltage control unit 502 is one or more voltage
controllers. In some embodiments, a voltage controller is
configured to selectively adjust the voltage of the memory
cell.
The gate of PMOS transistor P4 is connected to the source of first
voltage signal RGV_ENB. The gate of PMOS transistor P4 is
configured to receive the first voltage signal RGV_ENB. The source
of PMOS transistor P4 is connected to voltage source VDD. The drain
of PMOS transistor P4 is connected to the drain of NMOS transistor
N2 and memory cells 204 and 540. In some embodiments, the first
voltage signal RGV_ENB selectively turns on/off PMOS transistor P4.
In some embodiments, PMOS transistor P4 is configured to control
the second voltage signal CVSS. In some embodiments, the first
voltage signal RGV_ENB selectively turns on/off PMOS transistor P4
which selectively connects/disconnects the drain of NMOS transistor
N2 to voltage source VDD.
The gate of NMOS transistor N2 is connected to voltage source VDD.
The drain of NMOS transistor N2 is connected to the drain of PMOS
transistor P4 and memory cells 204, 540. The source of NMOS
transistor N2 is connected to ground.
FIG. 6A is a schematic diagram of a voltage control unit 600a in
accordance with one or more embodiments. Voltage control unit 600a
is an embodiment of the voltage control unit 502 shown in FIG. 5
with similar elements.
Voltage control unit 600a is configured to receive inverted first
voltage signal RGV_EN. Voltage control unit 600a is configured to
control a second voltage signal CVSS on CV line 504. Voltage
control unit 600a comprises an NMOS transistor N2 and an NMOS
transistor N3. In some embodiments, voltage control unit 600a is
one or more voltage controllers. In some embodiments, a voltage
controller is configured to selectively adjust the voltage of the
memory cell.
The gate of NMOS transistor N2 is connected to voltage source VDD.
The drain of NMOS transistor N2 is connected to the drain of PMOS
transistor P4 and memory cells 204, 540. The source of NMOS
transistor N2 is connected to ground.
The gate of NMOS transistor N3 is connected to the source of
inverted first voltage signal RGV_EN. The gate of NMOS transistor
N3 is configured to receive inverted first voltage signal RGV_EN.
The drain of NMOS transistor N3 is connected to voltage source VDD.
The source of NMOS transistor N3 is connected to the drain of NMOS
transistor N2 and memory cells 204 and 540. In some embodiments,
inverted first voltage signal RGV_EN selectively turns on/off NMOS
transistor N3. In some embodiments, NMOS transistor N3 is
configured to control the second voltage signal CVSS. In some
embodiments, inverted first voltage signal RGV_EN selectively turns
on/off NMOS transistor N3 which connects the drain of NMOS
transistor N2 to voltage source VDD.
FIG. 6B is a schematic diagram of a voltage control unit 600b in
accordance with one or more embodiments. Voltage control unit 600b
is an embodiment of the voltage control unit 502 shown in FIG. 5
with similar elements.
Voltage control unit 600b is configured to receive inverted first
voltage signal RGV_EN. Voltage control unit 600b is configured to
control second voltage signal CVSS on CV line 504. Voltage control
unit 600b comprises an NMOS transistor N2 and an NMOS transistor
N3. In some embodiments, voltage control unit 600b is one or more
voltage controllers. In some embodiments, a voltage controller is
configured to selectively adjust the voltage of the memory
cell.
NMOS transistor N2 is connected in a diode configuration such that
the gate of NMOS transistor N2 is connected to the drain of NMOS
transistor N2. The gate and drain of NMOS transistor N2 are
connected to the source of NMOS transistor N3 and memory cells 204,
540. The source of NMOS transistor N2 is connected to ground.
The gate of NMOS transistor N3 is connected to the source of
inverted first voltage signal RGV_EN. The gate of NMOS transistor
N3 is configured to receive inverted first voltage signal RGV_EN.
The drain of NMOS transistor N3 is connected to voltage source VDD.
The source of NMOS transistor N3 is connected to the drain of NMOS
transistor N2 and memory cells 204 and 540. In some embodiments,
inverted first voltage signal RGV_EN selectively turns on/off NMOS
transistor N3. In some embodiments, NMOS transistor N3 is
configured to control the second voltage signal CVSS. In some
embodiments, inverted first voltage signal RGV_EN selectively turns
on/off NMOS transistor N3 which connects the drain of NMOS
transistor N2 to voltage source VDD.
FIGS. 7A and 7B are waveform diagrams of signals applied to write
logic cell 500 of an SRAM for a write operation in accordance with
one or more embodiments. Curves 702a, 702b represent the signal on
the word line WL (e.g., word line WL 316 shown in FIG. 3A, first
word line A_WL 316a or second word line A_WL 328 shown in FIG. 3B
and write word line WWL 316' shown in FIG. 3C); curves 704a, 704b
represent inverted first voltage signal RGV_EN; curves 706a, 706b
represent the second voltage signal CVSS and curves 708a, 708b,
710a, 710b represent the signal on data nodes C/T of cross-coupled
inverters 302.
FIG. 7A is a waveform diagram of signals applied to write logic
cell 500 of an SRAM for a write operation in accordance with one or
more embodiments.
At time T1, curve 702a (e.g., word line signal WL) transitions from
a logically high signal to a logically low signal. In some
embodiments, when curve 702a transitions to a logically low signal,
the first pass gate 312 and the second pass gate 314 (as shown in
FIGS. 3A-3C) each turn-on connecting the bit line BL/bit line bar
BLB to the cross-coupled inverters 302. At time T1, curve 704a
(e.g., inverted first voltage signal RGV_EN) transitions from a
logically low signal to a logically high signal. At time T1, curve
706a (e.g., second voltage signal CVSS) transitions from a first
low signal level LOW1 to a second low signal level LOW2. At time
T1, curve 708a transitions from a first low signal level LOW1' to a
second low signal level LOW2' and curve 710a transitions from a
logically high signal to a second low signal level LOW2'. In some
embodiments, curves 708a, 710a represent the ability of
cross-coupled inverters 302 to transition from a low logical state
to a high logical state and vice versa for the storage of a unit of
data in memory cells 204 and 540.
In some embodiments, the first low signal level LOW1 is
substantially equal to VSS. In some embodiments, the second low
signal level LOW2 is substantially equal to VSS+.DELTA.Vcvss, where
.DELTA.Vcvss is a lifted voltage level. In some embodiments, the
second low signal level LOW2 is a first intermediate voltage level
which ranges from about the first low signal level LOW1 to about a
logically high signal. In some embodiments, the lifted voltage
level .DELTA.Vcvss ranges from about 0 volts to about 200 mV. In
some embodiments, voltage VSS is substantially equal to ground. In
some embodiments, voltage VSS is substantially equal to a negative
voltage supply.
In some embodiments, the first low signal level LOW1' is
substantially equal to voltage VSS. In some embodiments, the second
signal level LOW2' is substantially equal to VSS+.DELTA.V, where
.DELTA.V is a data voltage difference. In some embodiments, the
second low signal level LOW2' is a second intermediate voltage
level which ranges from about the first low signal level LOW1' to
about a logically high signal. In some embodiments, the data
voltage difference .DELTA.V ranges from about 0 volts to about 150
mV.
In some embodiments, a change in inverted first voltage signal
RGV_EN (e.g., curve 704a) or first voltage signal RGV_ENB, causes
PMOS transistor P4 shown in FIG. 5 (or NMOS transistor N3 shown in
FIGS. 7A and 7B) to turn on/off, resulting in a boost in second
control voltage signal CVSS. In some embodiments, a change in
inverted first voltage signal RGV_EN (e.g., curve 704a) or second
control voltage signal CVSS results in a change in curves 708a,
710a (e.g., the store data flip time of cross-coupled inverters
302) by data voltage difference .DELTA.V.
At time T2, curve 702a (e.g., word line signal WL) finishes
transitioning to a logically low signal. At time T2, curve 704a
(e.g., inverted first voltage signal RGV_EN) finishes transitioning
to a logically high signal. At time T2, curve 706a (e.g., second
voltage signal CVSS) finishes transitioning to a second low signal
level LOW2.
At time T4, curve 704a (e.g., inverted first voltage signal RGV_EN)
transitions from a logically high signal to a logically low signal.
At time T4, curve 706a (e.g., second voltage signal CVSS)
transitions from a second low signal level LOW2 to a first low
signal level LOW1. At time T4, curve 708a reaches a logically high
signal, and curve 710a transitions from a second low signal level
LOW2' to a first low signal level LOW1'.
At time T5, curve 704a (e.g., inverted first voltage signal RGV_EN)
finishes transitioning to a logically low signal. At time T5, curve
706a (e.g., second voltage signal CVSS) finishes transitioning to a
first low signal level LOW1. At time T5, curve 710a finishes
transitioning to a first low signal level LOW1'.
At time T8, curve 702a transitions to a logically high signal. In
some embodiments, when curve 702a transitions to a logically high
signal, the first pass gate 312 and the second pass gate 314 (as
shown in FIG. 3A-3C) each turn-off and disconnect the bit line
BL/bit line bar BLB from the cross-coupled inverters 302. In some
embodiments, a single write cycle of the word line is represented
by curve 702a.
FIG. 7B is a waveform diagram of signals applied to write logic
cell 500 of an SRAM for a write operation in accordance with one or
more embodiments.
At time T1, curve 702b (e.g., word line signal WL) transitions from
a logically high signal to a logically low signal.
At time T3, curve 704b (e.g., inverted first voltage signal RGV_EN)
transitions from a logically low signal to a logically high signal.
At time T3, curve 706b (e.g., second voltage signal CVSS)
transitions from a first low signal level LOW1 to a second low
signal level LOW2. After time T3, curve 708b transitions to a
logically high signal and curve 710b transitions from an
intermediate signal level to a second low signal level LOW2'. In
some embodiments, curves 708b, 710b represent the ability of
cross-coupled inverters 302 to transition from a low logical state
to a high logical state and vice versa for the storage of a unit of
data in memory cells 204 and 540.
At time T6, curve 704b (e.g., inverted first voltage signal RGV_EN)
transitions from a logically high signal to a logically low signal.
At time T6, curve 706b (e.g., second voltage signal CVSS)
transitions from a second low signal level LOW2 to a first low
signal level LOW1. At time T6, curve 710b transitions from a second
low signal level LOW2' to a first low signal level LOW1'.
At time T7, curve 704b (e.g., inverted first voltage signal RGV_EN)
finishes transitioning to a logically low signal. At time T7, curve
706b (e.g., second voltage signal CVSS) finishes transitioning to a
first low signal level LOW1. At time T7, curve 710b finishes
transitioning to a first low signal level LOW1'.
At time T8, curve 702a transitions to a logically high signal. In
some embodiments, when curve 702a transitions to a logically high
signal, the first pass gate 312 and the second pass gate 314 (as
shown in FIG. 3A-3C) each turn-off and disconnect the bit line
BL/bit line bar BLB from the cross-coupled inverters 302. In some
embodiments, a single write cycle of the word line is represented
by curve 702a.
As shown in FIGS. 7A and 7B, by controlling the timing of the
rising edge or the falling edge of the first voltage signal RGV_EN,
the rising edge or the falling edge of the second voltage signal
CVSS and the value of the second voltage signal CVSS are similarly
controlled. As shown in FIGS. 7A and 7B, by controlling the timing
of the rising edge or the falling edge of the first voltage signal
RGV_EN or second voltage signal CVSS, the store data flip time of
cross-coupled inverters 302 (e.g., curves 708a, 710a) is also
changed. In some embodiments, the pulse width of inverted first
control signal RGV_EN or first control signal RGV_ENB controls the
pulse width of second voltage signal CVSS. In some embodiments,
when curves 706a, 706b (e.g., second voltage signal CVSS)
transition to a voltage level greater than VSS, the NMOS
transistors 308 and 310 (shown in FIGS. 3A-3C) are weakened and the
operating region (e.g., VCCmin) of memory cells 204, . . . , 540
are improved. In some embodiments, the operating region (e.g.,
VCCmin) of memory cells 204, . . . , 540 are the minimum voltage at
which the memory cell can reliably operate.
FIG. 8A is a schematic diagram of a logic cell 800a in accordance
with one or more embodiments. Memory cell 204 is an embodiment of
memory cell 104 and memory cell 540 is an embodiment of memory cell
140 shown in FIG. 1. Word line WL[0] 206 is an embodiment of write
word line WWL[0] 102 shown in FIG. 1. Word line WL[M-1] 508 is an
embodiment of write word line WWL[M-1] 138 shown in FIG. 1. Bit
line BL 208 is an embodiment of write bit line WBL[0] 150 shown in
FIG. 1. Bit line bar BLB 210 is an embodiment of write bit line bar
WBLB[0] 152 shown in FIG. 1.
Logic cell 800a comprises memory cells 204, 540, word line control
unit 802, word line driver 804, footer line 806, negative word line
810, NMOS transistors N4[0], . . . N[M-1] where M is an integer
corresponding to the number of rows in memory cell array 100, word
lines WL[0] 206, . . . , WL[M-1] 508 where M is an integer
corresponding to the number of rows in the memory cell array, bit
line BL 208 and bit line bar 210.
Memory cell 204 is connected to word line control unit 802 by word
line driver 804, word line WL[0] 206, negative word line 810 and
footer line 806. Memory cell 540 is connected to word line control
unit 802 by word line driver 804 and word line WL[M-1] 508,
negative word line 810 and footer line 806. In some embodiments,
one word line control unit 802 is connected to one or more memory
cells 204, 540. In some embodiments, one or more word line control
units 802 are connected to at least one memory cell 204. In some
embodiments, word line driver 804 is connected to each of the
memory cells in memory cell array 100 by word lines WL[0] 206, . .
. , WL[M-1] 508.
Word line control unit 802 is configured to receive a clock signal
CLKW, a tracking control signal TM_NWL and a select control signal
NWL_TSEL. Word line control unit 802 is configured to send first
voltage control signal footer_enb to NMOS transistors N[0], . . . ,
N[M-1]. Word line control unit 802 is configured to control word
line driver 804 by the negative word line signal NVSS. Word line
control unit 802 comprises a timing unit 212 and a voltage control
unit 808.
Timing unit 212 is configured to receive clock signal CLKW,
tracking control signal TM_NWL and select control signal NWL_TSEL.
The clock signal CLKW is, e.g., a logically low signal or a
logically high signal. The tracking control signal TM_NWL is, e.g.,
a logically low signal or a logically high signal. In some
embodiments, the select control signal NWL_TSEL is, e.g., a
logically low signal or a logically high signal. In some
embodiments, select control signal NWL_TSEL is a multiple bit
signal with more than two logical states. Timing unit 212 is
configured to send a control signal to voltage control unit 808. In
some embodiments, the control signal sent to the voltage control
unit 808 is a version of the first voltage control signal
footer_enb prior to the inverters I1 and I2. The first voltage
control signal footer_enb is, e.g., a logically low signal or a
logically high signal. In some embodiments, timing unit 212 is
configured to control the timing of the word line control unit 802.
In some embodiments, timing unit 212 is configured to control the
pulse width of the first voltage control signal footer_enb. In some
embodiments, timing unit 212 is configured to control the rising
edge or the falling edge of the first voltage control signal
footer_enb. Timing unit 212 is connected to voltage control unit
808. Timing unit 212 includes three inputs; one input of timing
unit 212 is connected to the source of the clock signal CLKW, one
input of timing unit 212 is connected to the source of the tracking
control signal TM_NWL and one input of timing unit 212 is connected
to the source of the select control signal NWL_TSEL.
Voltage control unit 808 comprises inverter I1, inverter I2,
inverter I3, inverter I4 and PMOS transistor P5. Voltage control
unit 808 is configured to receive a signal from timing unit 212.
Voltage control unit 808 is configured to send first voltage
control signal footer_enb to NMOS transistors N4[0], . . . ,
N4[M-1]. Voltage control unit 808 is configured to control a
negative word line signal NVSS. In some embodiments, the negative
word line signal NVSS is a value ranging from about
VSS+.DELTA.Vnvss volts to about VSS volts, where .DELTA.Vnvss is a
negative voltage signal. In some embodiments, voltage VSS is
substantially equal to ground. In some embodiments, the negative
voltage signal .DELTA.Vnvss ranges from about -200 mV to about 0
volts. In some embodiments, a voltage control unit 808 is one or
more voltage controllers. In some embodiments, a voltage controller
is configured to selectively adjust the voltage of the memory
cell.
Inverter I1 is connected to timing unit 212 and inverter I2.
Inverter I1 is configured to receive a control signal from the
timing unit 212. Inverter I1 is configured to send an inverted
version of the control signal to inverter I2.
Inverter I2 is connected to inverter I1, inverter I3 and NMOS
transistors N4[0], . . . , N4[M-1]. Inverter I2 is configured to
receive the inverted version of the control signal from inverter
I1. Inverter I2 is configured to send a first voltage control
signal footer_enb to inverter I3 and NMOS transistors N4[0], . . .
, N4[M-1]. Inverter I2 is connected to NMOS transistors N4[0], . .
. , N4[M-1] by footer line 806.
Inverter I3 is connected to inverter I2, inverter I4 and NMOS
transistors N4[0], . . . , N4[M-1]. Inverter I3 is configured to
receive the first voltage control signal footer_enb from inverter
I3. Inverter I3 is configured to send an inverted version of the
first voltage control signal footer_enb to inverter I4.
Inverter I4 is connected to inverter I3 and PMOS transistor P5.
Inverter I4 is configured to receive the inverted version of the
first voltage control signal footer_enb from inverter I3. Inverter
I4 is configured to send a second voltage control signal NWL_enb to
PMOS transistor P5. In some embodiments, the second voltage control
signal NWL_enb is a delayed version of the first voltage control
signal footer_enb. The second voltage control signal NWL_enb is,
e.g., a logically low signal or a logically high signal.
The drain of PMOS transistor P5 is connected to the source of PMOS
transistor P5. The gate of PMOS transistor P5 is connected to the
drain of NMOS transistors N[0], . . . , N[M-1] and word line write
driver 804. In some embodiments, PMOS transistor P5 functions as a
capacitor since the drain and source terminals of the PMOS
transistor P5 are coupled together. In some embodiments, PMOS
transistor P5 is configured to control the negative word line
signal NVSS. In some embodiments, the second voltage control signal
NWL_enb controls the charging/discharging of the PMOS transistor
P5.
The gate of NMOS transistors N4[0], . . . , N4[M-1] are connected
to inverter I2 and inverter I3 by footer line 806. The gate of NMOS
transistors N4[0], . . . , N4[M-1] is configured to receive the
first voltage control signal footer_enb. The source of NMOS
transistors N4[0], . . . , N4[M-1] is connected to ground. The
drain of NMOS transistors N4[0], . . . , N4[M-1] is connected to
the gate of PMOS transistor P5 and word line driver 804. In some
embodiments, the first voltage control signal footer_enb
selectively turns on/off NMOS transistors N4[0], . . . , N4[M-1].
In some embodiments, NMOS transistors N4[0], . . . , N4[M-1] are
configured to control the negative word line signal NVSS. In some
embodiments, the first voltage control signal footer_enb and the
second voltage control signal NWL_enb controls the
charging/discharging of the PMOS transistor P5.
Word line driver 804 comprises inverters I11[0], . . . , I11[M-1]
where M is an integer corresponding to the number of rows in memory
cell array 100. Inverters I11[0], . . . , I11[M-1] are connected to
the drain of NMOS transistors N4[0], . . . , N4[M-1] and the gate
of PMOS transistor P5 by negative word line 810.
Inverters I11[0], . . . , I11[M-1] are configured to receive a data
signal D1. Inverters I11[0], . . . , I11[M-1] are configured to
receive the negative word line signal NVSS by negative word line
810. In some embodiments, inverters I11[0], . . . , I11[M-1] are
powered by negative word line signal NVSS. In some embodiments,
inverters I11[0], . . . , I11[M-1] are configured such that the
negative word line signal NVSS is connected to the operating
voltage terminal of inverters I11[0], . . . , I11[M-1]. Inverters
I11[0], . . . , I11[M-1] are configured to send a word line signal
WL on word lines WL[0] 206, . . . , WL[M-1] 508 to each of the
memory cells (e.g., memory cells 204, 540).
In some embodiments, the word line signal WL is a value ranging
from about VSS+.DELTA.Vw1 volts to about VSS volts, where
.DELTA.Vw1 is a negative voltage signal. In some embodiments, the
negative voltage signal .DELTA.Vw1 ranges from about -150 mV to
about 0 volts. In some embodiments, the negative voltage signal
.DELTA.Vw1 is less than the negative word line signal NVSS.
FIG. 8B is a schematic diagram of a logic cell 800b in accordance
with one or more embodiments. Logic cell 800b is an embodiment of
logic cell 800a with similar elements. In comparing FIGS. 8A and
8B, the word line driver 804 of FIG. 8A is replaced with the read
word line driver 804' of FIG. 8B, and the word lines WL[0] 206, . .
. , WL[M-1] 508 of FIG. 8A are replaced with the read word lines
RWL[0] 812, . . . , RWL[M-1] 814 of FIG. 8B.
Read word line driver 804' is an embodiment of word line driver
804. Read word lines RWL[0] 812, . . . , RWL[M-1] 814 are an
embodiment of the read word lines RWL[0] 180, . . . , RWL[M-1] 186
shown in FIG. 1. Read word lines RWL[0] 812, . . . , RWL[M-1] 814
connect the read word line driver 804' to the memory cells 204, . .
. , 540.
FIG. 9 is a waveform diagram of signals applied to write logic cell
800a or 800b of an SRAM in accordance with one or more
embodiments.
Curve 902 represents the signal on the word line WL (e.g., word
line WL 316 shown in FIG. 3A, first word line A_WL 316a or second
word line A_WL 328 shown in FIG. 3B, write word line WWL 316' or
read word line RWL 328' shown in FIG. 3C); curve 904 represents the
first voltage control signal footer_enb; curve 906 represents the
second voltage control signal NWL_enb; and curve 908 represents the
negative word line signal NVSS. FIG. 9 shows waveforms of various
signals when memory cells 204, 540 are accessed for a read or write
operation.
At time T1, curve 902 (e.g., word line signal WL or read word line
signal RWL) transitions from a logically high signal to a logically
low signal. In some embodiments, for a write operation, when curve
902 transitions to a logically low signal, the first pass gate 312
and the second pass gate 314 (as shown in FIG. 3A-3C) each turn-on
connecting the bit line BL/bit line bar BLB to the cross-coupled
inverters 302.
At time T2, curve 904 (e.g., first voltage control signal
footer_enb) starts transitioning from a logically high signal to a
logically low signal.
After time T2, curve 904 (e.g., first voltage control signal
footer_enb) finishes transitioning from a logically high signal to
a logically low signal. In some embodiments, when curve 904
transitions to a logically low signal, the NMOS transistors N4[0],
. . . . , N4[M-1] (as shown in FIG. 8) turn-off which disconnects
the gate of the PMOS transistor P5 from ground (e.g., VSS).
At time T3, curve 906 (e.g., second voltage control signal NWL_enb)
transitions from a logically high signal to a logically low signal.
At time T3, curve 908 (e.g., negative word line signal NVSS)
transitions from a second low signal level LOW2' to a first low
signal level LOW1'. In some embodiments, the second low signal
level LOW2' is an intermediate signal which ranges from about the
first low signal level LOW1' to about a logically high signal.
In some embodiments, the second signal level LOW2 is substantially
equal to voltage VSS. In some embodiments, the first signal level
LOW1 is substantially equal to VSS+.DELTA.Vw1, where .DELTA.Vw1 is
a negative voltage signal. In some embodiments, the second signal
level LOW2' is substantially equal to voltage VSS. In some
embodiments, the first signal level LOW1' is substantially equal to
VSS+.DELTA.Vnvss, where .DELTA.Vnvss is a negative voltage
signal.
In some embodiments, PMOS transistor P5 functions as a capacitor
since the source and drain are coupled together. In some
embodiments, a change in the first voltage control signal
footer_enb (e.g., curve 904) and the second voltage control signal
NWL_enb (e.g., curve 906), causes the PMOS transistor P5 to
discharge resulting in a change in the negative word line signal
NVSS (e.g., curve 908). In some embodiments, the change in the
first voltage control signal footer_enb (e.g., curve 904) directly
results in a change in the second voltage control signal NWL_enb
(e.g., curve 906). In some embodiments, the change in the first
voltage control signal footer_enb (e.g., curve 904) or the second
voltage control signal NWL_enb (e.g., curve 906), triggers a
corresponding change in both the negative word line signal NVSS
(e.g., curve 908) and the word line/read word line signal WL/RWL
(e.g., curve 902). In some embodiments, a change in the negative
word line signal NVSS (e.g., curve 908) results in a corresponding
change of the word line/read word line signal WL/RWL (e.g., curve
902).
At time T4, curve 906 (e.g., second voltage control signal NWL_enb)
finishes transitioning to a logically low signal. At time T4, curve
908 (e.g., boosted voltage signal BVDD) finishes transitioning to a
first low signal level LOW1'. At time T4, curve 902 (e.g., word
line signal WL or read word line signal RWL) transitions from a
second low signal level LOW2 to a first low signal level LOW1. In
some embodiments, the second low signal level LOW2 is an
intermediate signal which ranges from about the first low signal
level LOW1 to about a logically high signal.
At time T5, curve 902 (e.g., word line signal WL or read word line
signal RWL) finishes transitioning to a first low signal level
LOW1.
At time T6, curve 902 (e.g., word line signal WL or read word line
signal RWL) transitions to a logically high signal. In some
embodiments, for a write operation, when curve 902 transitions to a
logically high signal, the first pass gate 312 and the second pass
gate 314 (as shown in FIG. 3A-3C) each turn-off and disconnect the
bit line BL/bit line bar BLB from the cross-coupled inverters 302.
In some embodiments, a single read or write cycle of the word line
is represented by curve 902.
At time T7, curve 902 (e.g., word line signal WL or read word line
signal RWL) finishes transitioning to a logically high signal.
At time T8, curve 904 (e.g., first voltage control signal
footer_enb) transitions from a logically low signal to a logically
high signal.
At time T9, curve 906 (e.g., second voltage control signal NWL_enb)
transitions to a logically high signal. At time T9, curve 908
(e.g., boosted voltage signal BVDD) transitions to a second low
signal level LOW2'.
In some embodiments, curve 902 (e.g., word line signal WL or read
word line signal RWL) transitions to a voltage level less than
ground which strengthens the capability of first pass gate 312, the
second pass gate 314, third pass gate 322, fourth pass gate 324 and
read bit line transistor 324a (as shown in FIGS. 3A-3C). In some
embodiments, curve 902 (e.g., word line signal WL or read word line
signal RWL) transitions to a voltage level less than ground which
improves the operating region (e.g., VCCmin) of memory cells 204, .
. . , 540. In some embodiments, the operating region (e.g., VCCmin)
of memory cells 204, . . . , 540 is the minimum voltage at which
the memory cell can reliably operate.
FIG. 10 is a schematic diagram of a write logic cell 1000 in
accordance with one or more embodiments. Memory cell 204 is an
embodiment of memory cell 104 shown in FIG. 1. Word line WL[0] 206
is an embodiment of write word line WWL[0] 102 shown in FIG. 1. Bit
line BL 208 is an embodiment of write bit line WBL[0] 150 shown in
FIG. 1. Bit line bar BLB 210 is an embodiment of write bit line bar
WBLB[0] 152 shown in FIG. 1.
Write logic cell 1000 comprises a voltage control unit 1002, an
inverter I12, memory cell 204, word line WL[0] 206, bit line BL 208
and bit line bar BLB 210. Memory cell 204 is connected to a bit
line BL 208 and a bit line bar BLB 210.
Voltage control unit 1002 is configured to receive a first signal
EN/ENB. In some embodiments, first signal EN/ENB is, e.g., a
logically low signal or a logically high signal. In some
embodiments, first signal EN/ENB is, e.g., a pulse signal that
transitions to and from a logically low signal or a logically high
signal. In some embodiments, first signal EN/ENB is an
enable/disable signal which switches the voltage control unit 1002
on/off. Voltage control unit 1002 is configured to receive a second
signal VLWL. In some embodiments, second signal VLWL is, e.g., a
logically low signal or a logically high signal. In some
embodiments, second signal VLWL is a voltage signal connected to
voltage source VDD. Voltage control unit 1002 is configured to
control a word line signal WL on word line WL[0] 206. In some
embodiments, voltage control unit 1002 is configured to change the
word line signal WL on word line WL[0] 206. The voltage control
unit 1002 is connected to inverter I12 and memory cell 204 by word
line WL[0] 206. In some embodiments, voltage control unit 1002 is
connected to one or more memory cells in memory cell array 100. In
some embodiments, a plurality of voltage control units 1002 are
each connected to one or more memory cells in memory cell array
100. In some embodiments, voltage control unit 1002 is one or more
voltage controllers. In some embodiments, a voltage controller is
configured to selectively adjust the voltage of the memory cell
204.
Inverter I12 is connected to memory cell 204 and voltage control
unit 1002 by the word line WL[0] 206. Inverter I12 is configured to
receive a word line signal WLN. In some embodiments, word line
signal WLN is, e.g., a logically low signal or a logically high
signal. Inverter I12 is configured to send word line signal WL to
memory cell 204 and voltage control unit 1002. In some embodiments,
word line signal WL is an inverted version of word line signal
WLN.
FIG. 11A is a schematic diagram of a voltage control unit 1100a in
accordance with one or more embodiments. Voltage control unit 1100a
is an embodiment of the voltage control unit 1002 shown in FIG. 10
with similar elements.
Voltage control unit 1100a is configured to receive first signal EN
and second signal VLWL. Voltage control unit 1100a is configured to
control a word line signal WL on word line WL[0] 206. Voltage
control unit 1100a comprises an NMOS transistor N5. In some
embodiments, voltage control unit 1100a is one or more voltage
controllers. In some embodiments, a voltage controller is
configured to selectively adjust the voltage of the memory
cell.
The gate of NMOS transistor N5 is connected to the source of first
signal EN. In some embodiments, first signal EN is an
enable/disable signal which switches the NMOS transistor N5 on/off.
The drain of NMOS transistor N5 is connected to the source of
second signal VLWL. In some embodiments, the second signal VLWL is
a voltage received from a voltage source VDD. The source of NMOS
transistor N5 is connected to word line WL[0] 206. NMOS transistor
N5 is configured to control word line signal WL on word line WL[0]
206. In some embodiments, NMOS transistor N5 is configured to
change the word line signal WL on word line WL[0] 206.
FIG. 11B is a schematic diagram of a voltage control unit 1100b in
accordance with one or more embodiments. Voltage control unit 1100b
is an embodiment of the voltage control unit 1002 shown in FIG. 10
with similar elements.
Voltage control unit 1100b is configured to receive inverted first
signal ENB and second signal VLWL. Voltage control unit 1100b is
configured to control a word line signal WL on word line WL[0] 206.
Voltage control unit 1100b comprises a PMOS transistor P6. In some
embodiments, voltage control unit 1100b is one or more voltage
controllers. In some embodiments, a voltage controller is
configured to selectively adjust the voltage of the memory
cell.
The gate of PMOS transistor P6 is connected to the source of
inverted first signal ENB. In some embodiments, inverted first
signal ENB is an enable/disable signal which switches the PMOS
transistor P6 on/off. The source of PMOS transistor P6 is connected
to the source of second signal VLWL. In some embodiments, the
second signal VLWL is a voltage received from a voltage source VDD.
The drain of PMOS transistor P6 is connected to word line WL[0]
206. PMOS transistor P6 is configured to control word line signal
WL on word line WL[0] 206. In some embodiments, PMOS transistor P6
is configured to change the word line signal WL on word line WL[0]
206.
FIG. 11C is a schematic diagram of a voltage control unit 1100c in
accordance with one or more embodiments. Voltage control unit 1100c
is an embodiment of the voltage control unit 1002 shown in FIG. 10
with similar elements.
Voltage control unit 1100c is configured to receive inverted first
signal ENB. Voltage control unit 1100c is connected to voltage
source VDD. Voltage control unit 1100c is configured to control a
word line signal WL on word line WL[0] 206. Voltage control unit
1100c comprises PMOS transistor P6 and PMOS transistor P7. In some
embodiments, a voltage control unit 1100c is one or more voltage
controllers. In some embodiments, a voltage controller is
configured to selectively adjust the voltage of the memory
cell.
The gate of PMOS transistor P6 is connected to the source of
inverted first signal ENB. In some embodiments, inverted first
signal ENB is an enable/disable signal which switches the PMOS
transistor P6 on/off. The source of PMOS transistor P6 is connected
to the drain and gate of PMOS transistor P7. The drain of PMOS
transistor P6 is connected to word line WL[0] 206. PMOS transistor
P6 is configured to control word line signal WL on word line WL[0]
206. In some embodiments, PMOS transistor P6 is configured to
change the word line signal WL on word line WL[0] 206.
The gate of PMOS transistor P7 is connected to the drain of PMOS
transistor P7 and the source of PMOS transistor P6. PMOS transistor
P7 is connected in a diode configuration such that the gate of PMOS
transistor P7 is connected to the drain of PMOS transistor P7. The
source of PMOS transistor P7 is connected to voltage source
VDD.
FIGS. 12A, 12B and 12C are waveform diagrams of signals applied to
write logic cell 1000 of an SRAM for a write operation in
accordance with one or more embodiments. Curve 1202 represents the
inverted word line signal WLN (shown in FIG. 10); curves 1204a,
1204b, 1204c represent the word line signal WL; and curves 1206a,
1206b, 1206c represent the first signal EN.
FIG. 12A is a waveform diagram of signals applied to write logic
cell 1000 of an SRAM for a write operation in accordance with one
or more embodiments.
At time T1, curve 1202 (e.g., inverted word line signal WLN)
transitions from a logically low signal to a logically high signal.
At time T1, curve 1204a (e.g., word line signal WL) transitions
from a logically high signal to a first low signal level LOW1. In
some embodiments, the first low signal level LOW1 is substantially
equal to voltage VSS. In some embodiments, voltage VSS is
substantially equal to ground. In some embodiments, when curve
1204a transitions to a first low signal level LOW1, the first pass
gate 312 and the second pass gate 314 (as shown in FIGS. 3A-3C)
each turn-on connecting the bit line BL/bit line bar BLB to the
cross-coupled inverters 302.
At time T2, curve 1202 (e.g., inverted word line signal WLN)
finishes transitioning to a logically high signal. At time T2,
curve 1204a (e.g., word line signal WL) finishes transitioning to a
first low signal level LOW1.
At time T3, curve 1206a (e.g., first signal EN) transitions from a
logically low signal to a logically high signal. In some
embodiments, when first signal EN transitions to a logically high
signal, voltage control unit 1000 switches on (e.g. NMOS transistor
N5 shown in FIG. 11A or PMOS transistor P6 shown in FIGS. 11B and
11C) which boosts or lifts the word line signal WL by .DELTA.Vw1
volts. At time T3, curve 1204a (e.g., word line signal WL)
transitions from a first low signal level LOW1 to a second low
signal level LOW2. In some embodiments, the second low signal level
LOW2 is substantially equal to VSS+.DELTA.Vw1, where .DELTA.Vw1 is
the lifted voltage level. In some embodiments, the second low
signal level LOW2 is an intermediate voltage level which ranges
from about the first low signal level LOW1 to about a logically
high signal. In some embodiments, the lifted voltage level
.DELTA.Vw1 ranges from about 0 volts to about 150 mV. In some
embodiments, a change in the first signal EN (e.g., curve 1206a) or
curve 1202 (e.g. inverted word line signal WLN) results in a change
in curve 1204a (e.g., word line signal WL).
At time T4, curve 1206a (e.g., word line signal WL) finishes
transitioning to a logically high signal. At time T4, curve 1204a
(e.g., word line signal WL) finishes transitioning to a second low
signal level LOW2. In some embodiments, by changing the word line
signal WL to second low signal level LOW2, the first pass gate 312
and the second pass gate 314 (as shown in FIGS. 3A-3C) are weakened
which reduces noise from the bit line BL and bit line bar BLB.
At time T7, curve 1202 (e.g., inverted word line signal WLN)
transitions from a logically high signal to a logically low signal.
At time T7, curve 1204a (e.g., word line signal WL) transitions
from a second low signal level LOW2 to a logically high signal.
At time T8, curve 1202 (e.g., inverted word line signal WLN)
finishes transitioning to a logically low signal. At time T8, curve
1204a (e.g., word line signal WL) finishes transitioning to a
logically high signal.
At time T9, curve 1206 (e.g., first signal EN) transitions to a
logically low signal.
FIG. 12B is a waveform diagram of signals applied to write logic
cell 1000 of an SRAM for a write operation in accordance with one
or more embodiments.
At time T1, curve 1202 (e.g., inverted word line signal WLN)
transitions from a logically low signal to a logically high signal.
At time T1, curve 1204b (e.g., word line signal WL) transitions
from a logically high signal to a second low signal level LOW2. At
time T1, curve 1206b (e.g., first signal EN) transitions from a
logically low signal to a logically high signal. In some
embodiments, when curve 1206b (e.g., first signal EN) transitions
to a logically high signal, voltage control unit 1000 switches on
(e.g. NMOS transistor N5 shown in FIG. 11A or PMOS transistor P6
shown in FIGS. 11B and 11C) which boosts or lifts the word line
signal WL by .DELTA.Vw1 volts, and voltage control unit 1000
adjusts curve 1204b (e.g., the word line signal WL) from reaching
the first low signal level LOW1. In this example, curve 1204b
(e.g., the word line signal WL) reaches second low signal level
LOW2. In some embodiments, when curve 1204b reaches a second low
signal level LOW2, the first pass gate 312 and the second pass gate
314 (as shown in FIGS. 3A-3C) each partially turn-on and partially
connect the bit line BL/bit line bar BLB to the cross-coupled
inverters 302. In some embodiments, a change in curve 1206b (e.g.,
first signal EN) or curve 1202 (e.g., inverted word line signal
WLN) results in a change in curve 1204b (e.g., word line signal
WL).
At time T2, curve 1202 (e.g., inverted word line signal WLN)
finishes transitioning to a logically high signal. At time T2,
curve 1204b (e.g., word line signal WL) finishes transitioning to a
second low signal level LOW2. At time T2, curve 1206b (e.g., first
signal EN) finishes transitioning to a logically high signal.
At time T3, curve 1206b (e.g., first signal EN) transitions from a
logically high signal to a logically low signal. At time T3, curve
1204b (e.g., word line signal WL) transitions from a second low
signal level LOW2 to a first low signal level LOW1. In some
embodiments, when curve 1206b (e.g., first signal EN) transitions
to a logically low signal, voltage control unit 1000 switches off
(e.g., NMOS transistor N5 shown in FIG. 11A or PMOS transistor P6
shown in FIGS. 11B and 11C) which allows the word line signal WL to
reach the first low signal level LOW1.
At time T4, curve 1206b (e.g., first signal EN) finishes
transitioning to a logically low signal. At time T4, curve 1204b
(e.g., word line signal WL) finishes transitioning to a first low
signal level LOW1.
At time T7, curve 1202 (e.g., inverted word line signal WLN)
transitions from a logically high signal to a logically low signal.
At time T7, curve 1204b (e.g., word line signal WL) transitions
from a first low signal level LOW1 to a logically high signal.
At time T8, curve 1202 (e.g., inverted word line signal WLN)
finishes transitioning to a logically low signal. At time T8, curve
1204b (e.g., word line signal WL) finishes transitioning to a
logically high signal.
FIG. 12C is a waveform diagram of signals applied to write logic
cell 1000 of an SRAM for a write operation in accordance with one
or more embodiments.
At time T1, curve 1202 (e.g., inverted word line signal WLN)
transitions from a logically low signal to a logically high signal.
At time T1, curve 1204c (e.g., word line signal WL) transitions
from a logically high signal to a first low signal level LOW1. In
some embodiments, when curve 1204c transitions to a first low
signal level LOW1, the first pass gate 312 and the second pass gate
314 (as shown in FIGS. 3A-3C) each turn-on connecting the bit line
BL/bit line bar BLB to the cross-coupled inverters 302.
At time T2, curve 1202 (e.g., inverted word line signal WLN)
finishes transitioning to a logically high signal. At time T2,
curve 1204c (e.g., word line signal WL) finishes transitioning to a
first low signal level LOW1.
At time T3, curve 1206c (e.g., first signal EN) transitions from a
logically low signal to a logically high signal. In some
embodiments, when curve 1206c (e.g., first signal EN) transitions
to a logically high signal, voltage control unit 1000 switches on
(e.g. NMOS transistor N5 shown in FIG. 11A or PMOS transistor P6
shown in FIGS. 11B and 11C) which boosts or lifts the word line
signal WL by .DELTA.Vw1 volts. At time T3, curve 1204c (e.g., word
line signal WL) transitions from a first low signal level LOW1 to a
second low signal level LOW2. In some embodiments, when curve 1204c
reaches a second low signal level LOW2, the first pass gate 312 and
the second pass gate 314 (as shown in FIGS. 3A-3C) are partially
turned-on and partially connected to the bit line BL/bit line bar
BLB to the cross-coupled inverters 302. In some embodiments, a
change in curve 1206c (e.g., first signal EN) or curve 1202 (e.g.,
inverted word line signal WLN) results in a change in curve 1204c
(e.g., word line signal WL).
At time T4, curve 1204c (e.g., word line signal WL) finishes
transitioning to a second low signal level LOW2. At time T4, curve
1206c (e.g., first signal EN) finishes transitioning to a logically
high signal.
At time T5, curve 1206c (e.g., first signal EN) transitions from a
logically high signal to a logically low signal. At time T5, curve
1204c (e.g., word line signal WL) transitions from a second low
signal level LOW2 to a first low signal level LOW1. In some
embodiments, when curve 1206c (e.g., first signal EN) transitions
to a logically low signal, voltage control unit 1000 switches off
(e.g., NMOS transistor N5 shown in FIG. 11A or PMOS transistor P6
shown in FIGS. 11B and 11C) which allows the word line signal WL to
reach the first low signal level LOW1.
At time T6, curve 1206c (e.g., first signal EN) finishes
transitioning to a logically low signal. At time T6, curve 1204c
(e.g., word line signal WL) finishes transitioning to a first low
signal level LOW1.
At time T7, curve 1202 (e.g., inverted word line signal WLN)
transitions from a logically high signal to a logically low signal.
At time T7, curve 1204c (e.g., word line signal WL) transitions
from a first low signal level LOW1 to a logically high signal.
At time T8, curve 1202 (e.g., inverted word line signal WLN)
finishes transitioning to a logically low signal. At time T8, curve
1204c (e.g., word line signal WL) finishes transitioning to a
logically high signal.
As shown in FIGS. 12A, 12B and 12C, by controlling the timing of
the rising edge or the falling edge of the signal EN, the value of
the word line signal WL is similarly controlled. As shown in FIGS.
12A, 12B and 12C, by controlling the pulse width of signal EN, the
length of time the word line signal WL is raised or lifted up to
the second low signal LOW2 is controlled. As shown in FIG. 12A, the
word line WL[0] turn on slew rate is improved when compared with
memory cells embodiments not utilizing the voltage control unit
1000. As shown in FIG. 12B, by delaying the word line WL[0]
transition to a logically low level, noise disturbances are reduced
from read currents. As shown in FIG. 12C, by combining the features
of FIGS. 12A and 12B, the word line WL[0] turn on slew rate is
improved and noise disturbances are reduced from read currents.
FIG. 13A is a schematic diagram of a read logic cell 1300a in
accordance with one or more embodiments. Read logic cell 1300a is
an embodiment of the write logic cell 1000 shown in FIG. 10 with
similar elements. In comparing FIGS. 10 and 13A, the word line
WL[0] 206 of FIG. 10 is replaced with the write word line WWL
316'.
Voltage control unit 1100a is an embodiment of voltage control unit
1002 shown in FIG. 11A. In this example, read word line signal RWLB
is an embodiment of first signal EN shown in FIG. 11A. Write word
line WWL 316' is an embodiment of word line 316 shown in FIG. 3a.
Read word line RWL 328' is an embodiment of read word line 328
shown in FIG. 3a. Inverter I12a is an embodiment of inverter I12
shown in FIG. 10.
Write logic cell 1300a comprises a voltage control unit 1100a,
inverter I12a, inverter I12b, memory cell 204, write word line WWL
316' and read word line RWL 328'. For simplicity, memory cell 204
is not shown in FIG. 13A.
Voltage control unit 1100a is configured to receive a first signal
RWLB by the gate of NMOS transistor N5. In some embodiments, first
signal RWLB is, e.g., a logically low signal or a logically high
signal. In some embodiments, first signal RWLB is, e.g., a pulse
signal that transitions to and from a logically low signal or a
logically high signal. In some embodiments, first signal RWLB is an
enable/disable signal which switches the voltage control unit 1100a
on/off. Voltage control unit 1100a is connected to voltage source
VDD by the drain of NMOS transistor N5. Voltage control unit 1100a
is connected to write word line WWL 316' by the source of NMOS
transistor N5. Voltage control unit 1100a is configured to control
a write word line signal WWL on write word line WL 316' in response
to signals received from the first signal RWLB. In some
embodiments, voltage control unit 1100a is configured to change the
write word line signal WWL on write word line WWL 316'. The voltage
control unit 1100a is connected to inverter I12a, inverter I12b,
write word line WWL 316', read word line RWL 328' and memory cell
204 (not shown). In some embodiments, voltage control unit 1100a is
connected to one or more memory cells in memory cell array 100. In
some embodiments, a plurality of voltage control units 1100a are
each connected to one or more memory cells in memory cell array
100.
Inverter I12a is connected to memory cell 204 (not shown) and
voltage control unit 1100a. Inverter I12a is configured to receive
a write word line signal WWLB. In some embodiments, write word line
signal WWLB is, e.g., a logically low signal or a logically high
signal. Inverter I12a is configured to send write word line signal
WWL to memory cell 204 (no shown) and voltage control unit 1100a.
In some embodiments, write word line signal WWL is an inverted
version of write word line signal WWLB.
Inverter I12b is connected to memory cell 204 (not shown) and
voltage control unit 1100a by the read word line RWL 328'. Inverter
I12b is configured to receive a read word line signal RWLB. In some
embodiments, read word line signal RWLB is, e.g., a logically low
signal or a logically high signal. Inverter I12b is configured to
send read word line signal RWL to memory cell 204 (not shown). In
some embodiments, read word line signal RWLB is an inverted version
of read word line signal RWL.
The read word line signal RWLB controls the voltage control unit
1100a by switching on/off the gate of NMOS transistor N5. In some
embodiments, switching on/off the gate of NMOS transistor N5
results in a change of the write word line signal WWL on write word
line WL 316'.
FIG. 13B is a schematic diagram of a read logic cell 1300b in
accordance with one or more embodiments. Read logic cell 1300b is
an embodiment of the read logic cell 1300a shown in FIG. 13A with
similar elements. Read logic cell 1300b includes each of the
elements of read logic cell 1300a, but read logic cell 1300b also
comprises an inverter I13. For simplicity, memory cell 204 is not
shown in FIG. 13B.
Inverter I12b is connected to memory cell 204 (not shown) and
inverter I13. Inverter I12b is configured to receive a read word
line signal RWLB. Inverter I12b is configured to send read word
line signal RWL to inverter I13. Inverter I12b is configured to
send read word line signal RWL to memory cell 204 (not shown). In
some embodiments, read word line signal RWLB is an inverted version
of read word line signal RWL.
Inverter I13 is connected to memory cell 204 (not shown), inverter
I12a, inverter I12b and voltage control unit 1100a. Inverter I13 is
configured to receive a read word line signal RWL. In some
embodiments, read word line signal RWL is, e.g., a logically low
signal or a logically high signal. Inverter I13 is configured to
send a delayed version of read word line signal RWLB to voltage
control unit 1100a.
The delayed version of the read word line signal RWLB controls the
voltage control unit 1100a by switching on/off the gate of NMOS
transistor N5. In some embodiments, switching on/off the gate of
NMOS transistor N5 results in a change of the write word line
signal WWL on write word line WL 316'.
FIG. 14A is a waveform diagram of signals applied to read logic
cells 1300a and 1300b of an SRAM when the voltage control unit
1100a is not operational in accordance with one or more
embodiments. FIG. 14B is a waveform diagram of signals applied to
read logic cells 1300a and 1300b of an SRAM in accordance with one
or more embodiments. Curve 1402 represents the read word line
signal RWL (shown in FIGS. 13A and 13B); curves 1404a, 1404b
represent the write word line signal WWL; curves 1406a, 1406b
represent the signal on data node C of cross-coupled inverters 302;
curve 1408 represents the signal on data node T of cross-coupled
inverters 302; and curve 1410 represent the read bit line RBL
(shown in FIGS. 1 and 3C) when reading a "1"; and curves 1412a,
1412b represent the read bit line RBL (shown in FIGS. 1 and 3C)
when reading a "0".
FIG. 14A is a waveform diagram of signals applied to read logic
cells 1300a and 1300b of an SRAM when the voltage control unit
1100a is not operational in accordance with one or more
embodiments. In some embodiments, the voltage control unit 1100a is
not operational if the gate of NMOS transistor N5 (shown in FIGS.
13A and 13B) is disconnected from the read word line RWLB or
RWL.
At time T1, curve 1402 (e.g., read word line signal RWL)
transitions from a logically high signal to a logically low signal.
At time T1, curve 1404a (e.g., write word line signal WWL)
transitions from a logically high signal to a logically low signal.
At time T1, curve 1406a (e.g., signal at node C of cross-coupled
inverters 302) transitions from a logically high signal to a
logically low signal. At time T1, curve 1410 (e.g., read bit line
signal RBL is a "1") transitions from a logically low signal to a
logically high signal. At time T1, curve 1412a (e.g., read bit line
signal RBL is a "0") transitions from a logically low signal to a
logically high signal.
At time T2, curve 1402 (e.g., read word line signal RWL) finishes
transitioning to a logically low signal. At time T2, curve 1404a
(e.g., write word line signal WWL) finishes transitioning to a
logically low signal. At time T2, curve 1406a (e.g., signal at node
C of cross-coupled inverters 302) finishes transitioning to a
logically low signal. At time T2, curve 1410 (e.g., read bit line
signal RBL is a "1") finishes transitioning to a logically low
signal.
At time T3, curve 1412a (e.g., read bit line signal RBL is a "0")
finishes transitioning to a logically low signal. In some
embodiments, from time T2 through T3, a voltage difference
.DELTA.Vrb1 is observed between curve 1410 and curve 1412a. In some
embodiments, the voltage difference .DELTA.Vrb1 represents a
voltage level difference associated with observing a logical "0"
and a logical "1" in memory cell 204.
At time T4, curve 1402 (e.g., read word line signal RWL)
transitions from a logically low signal to a logically high
signal.
At time T6, curve 1402 (e.g., read word line signal RWL) finishes
transitioning to a logically high signal. At time T6, curve 1404a
(e.g., write word line signal WWL) transitions from a logically low
signal to a logically high signal. At time T6, curve 1406a (e.g.,
signal at node C of cross-coupled inverters 302) transitions from a
logically low signal to a logically high signal.
At time T7, curve 1404a (e.g., write word line signal WWL) finishes
transitioning to a logically high signal. At time T7, curve 1406a
(e.g., signal at node C of cross-coupled inverters 302) finishes
transitioning to a logically high signal.
FIG. 14B is a waveform diagram of signals applied to read logic
cells 1300a and 1300b of an SRAM in accordance with one or more
embodiments.
At time T1, curve 1402 (e.g., read word line signal RWL)
transitions from a logically high signal to a logically low signal.
At time T1, curve 1404b (e.g., write word line signal WWL)
transitions from a logically high signal to a second low signal
level LOW2. At time T1, curve 1406b (e.g., signal at node C of
cross-coupled inverters 302) transitions from a logically high
signal to a second low signal level LOW2'. At time T1, curve 1410
(e.g., read bit line signal RBL is a "1") transitions from a
logically low signal to a logically high signal. At time T1, curve
1412b (e.g., read bit line signal RBL is a "0") transitions from a
logically low signal to a logically high signal. In some
embodiments, when read word line signal RWL transitions to a
logically low signal, inverted read word line signal RWLB
transitions to a logically high signal, and voltage control unit
1100a switches on (e.g. NMOS transistor N5 shown in FIGS. 13A and
13B) which boosts or lifts the write word line signal WWL by
.DELTA.Vw1 volts.
At time T2, curve 1402 (e.g., read word line signal RWL) finishes
transitioning to a logically low signal. At time T2, curve 1404b
(e.g., write word line signal WWL) finishes transitioning to second
low signal level LOW2. At time T2, curve 1406b (e.g., signal at
node C of cross-coupled inverters 302) finishes transitioning to
second low signal level LOW2'. At time T2, curve 1410 (e.g., read
bit line signal RBL is a "1") finishes transitioning to a logically
low signal.
At time T4, curve 1402 (e.g., read word line signal RWL)
transitions from a logically low signal to a logically high signal.
At time T4, curve 1404b (e.g., write word line signal WWL)
transitions from a second low signal level LOW2 to a first low
signal level LOW1. At time T4, curve 1406b (e.g., signal at node C
of cross-coupled inverters 302) transitions from second low signal
level LOW2' to a first low signal level LOW1'. In some embodiments,
the second low signal level LOW2 is an intermediate voltage level
which ranges from about the first low signal level LOW1 to about a
logically high signal. In some embodiments, the second low signal
level LOW2' is an intermediate voltage level which ranges from
about the first low signal level LOW1' to about a logically high
signal. In some embodiments, the first low signal level LOW1 is
substantially equal to VSS. In some embodiments, the first low
signal level LOW1' is substantially equal to VSS. In some
embodiments, voltage VSS is substantially equal to ground. In some
embodiments, the difference between the first low signal LOW1 and
the second low signal LOW2 is substantially equal to the lifted
voltage level .DELTA.Vw1' (e.g., as shown in FIGS. 12A, 12B and
12C). In some embodiments, the difference between the first low
signal LOW1' and the second low signal LOW2' is substantially equal
to the data voltage difference .DELTA.V (e.g., as shown in FIGS. 7A
and 7B). In some embodiments, when read word line signal RWL
transitions to a logically high signal, inverted read word line
signal RWLB transitions to a logically low signal, and voltage
control unit 1100a switches off (e.g., NMOS transistor N5 shown in
FIGS. 13A and 13B) which allows the word line signal WL to reach
the first low signal level LOW1.
At time T5, curve 1404b (e.g., write word line signal WWL) finishes
transitioning to first low signal level LOW1. At time T5, curve
1406b (e.g., signal at node C of cross-coupled inverters 302)
finishes transitioning to first low signal level LOW1'.
At time T6, curve 1402 (e.g., read word line signal RWL) finishes
transitioning to a logically high signal. At time T6, curve 1404b
(e.g., write word line signal WWL) transitions from first low
signal level LOW1 to a logically high signal. At time T6, curve
1406b (e.g., signal at node C of cross-coupled inverters 302)
transitions from first low signal level LOW1' to a logically high
signal. At time T6, curve 1412b (e.g., read bit line signal RBL is
a "0") finishes transitioning to a logically high signal. In some
embodiments, from time T1 through T6, a voltage difference
.DELTA.Vrb1' is observed between curve 1410 and curve 1412b. In
some embodiments, the voltage difference .DELTA.Vrb1' represents
the voltage level difference associated with observing a logical
"0" and a logical "1" in memory cell 204.
At time T7, curve 1404b (e.g., write word line signal WWL) finishes
transitioning to a logically high signal. At time T7, curve 1406b
(e.g., signal at node C of cross-coupled inverters 302) finishes
transitioning to a logically high signal.
As shown in FIGS. 14A and 14B, by controlling the timing of the
rising edge or the falling edge of the read word line signal RWL,
the value of the write word line signal WWL or the signal at node C
of cross-coupled inverters 302 are similarly controlled. As shown
in FIGS. 14A and 14B, by controlling the pulse width of read word
line signal RWL, the length of time the write word line signal WWL
is raised or lifted up to the second low signal LOW2 is controlled.
Similarly, by controlling the pulse width of read word line signal
RWL, the length of time the signal at node C of cross-coupled
inverters 302 is raised or lifted up to the second low signal LOW2'
is controlled. As shown in FIGS. 14A and 14B, by controlling the
signal at node C of cross-coupled inverters 302 or the read word
line RWL, the read bit line signal RBL is controlled. As shown in
FIGS. 14A and 14B, the read bit line signal RBL (e.g., curve 1412b)
transitions slower to the logically high level, when compared with
the read bit line signal RBL (e.g., curve 1412a) resulting in a
voltage difference .DELTA.Vrb1' that is greater than the voltage
difference .DELTA.Vrb1. In some embodiments, a voltage difference
.DELTA.Vrb1' that is greater than the voltage difference
.DELTA.Vrb1 results in improved static noise margin and logical "0"
read detection by memory cells.
FIG. 15 is a flow chart of a method 1500 of controlling an SRAM in
accordance with some embodiments. Method 1500 begins with
pre-charging at least one data line in operation 1502. Pre-charging
at least one data line comprises setting a voltage level on the at
least one data line to a reference voltage. In some embodiments,
the reference voltage includes a logically high signal. In some
embodiments, the reference voltage includes a logically low
signal.
In some embodiments, the at least one data line includes word line
WL (e.g., word line WL 206 shown in FIG. 2A, word line WL 316 shown
in FIG. 3A, first word line A_WL 316a and second word line B_WL 328
shown in FIG. 3B, write word line WWL 316' shown in FIGS. 3C and
13A-13B, word lines WL 206, . . . , WL 508 shown in FIGS. 5, 8A,
10, 11A-11C, read word line RWL 328' shown in FIGS. 3A and 13B, and
read word lines RWL 812, . . . , RWL 814 shown in FIG. 8B).
In some embodiments, the at least one data line includes bit line
BL (e.g., bit line BL 208 shown in FIG. 2A, bit line BL 318 shown
in FIG. 3A, first bit line A_BL 318a and second bit line B_BL 318b
shown in FIG. 3B, write bit line WBL 318' shown in FIG. 3C, read
bit line RBL 326' shown in FIG. 3C).
In some embodiments, the at least one data line includes bit line
bar BLB (e.g., bit line bar BLB 210 shown in FIG. 2A, bit line bar
BLB 320 shown in FIG. 3A, first bit line bar A_BLB 320a and second
bit line bar B_BLB 326 shown in FIG. 3B, and write bit line bar
WBLB 320' shown in FIG. 3C)
In some embodiments, the at least one data line includes data line
CV (e.g., CV line 504 shown in FIG. 5).
Method 1500 continues with operation 1504 in which a voltage
control unit is activated. In some embodiments, the voltage control
unit is voltage control unit 214 (shown in FIG. 2A). In some
embodiments, the voltage control unit is voltage control unit 214'
(shown in FIG. 2B). In some embodiments, the voltage control unit
is voltage control unit 502 (shown in FIG. 5). In some embodiments,
the voltage control unit is voltage control unit 808 (shown in
FIGS. 8A-8B). In some embodiments, the voltage control unit is
voltage control unit 1002 (shown in FIG. 10). In some embodiments,
the voltage control unit is voltage control unit 1100a (shown in
FIG. 11A), voltage control unit 1100b (shown in FIG. 11B) or
voltage control unit 1100c (shown in FIG. 11C).
In some embodiments, the activating the voltage control unit
comprises receiving at least one control signal. In some
embodiments, the activating the voltage control unit comprises
sending at least one control signal.
In some embodiments, the at least one control signal includes first
voltage control signal header_enb, second voltage control signal
BBL_en or boosted voltage signal BVDD (shown in FIG. 4). In some
embodiments, the at least one control signal includes first voltage
signal RGV_EN, inverted first voltage signal RGV_ENB (shown in
FIGS. 5, 6A-6B and 7A-7B). In some embodiments, the at least one
control signal includes first voltage control signal footer_enb,
second voltage control signal NWL_enb or negative word line signal
NVSS (shown in FIGS. 8A-8B and 9). In some embodiments, the at
least one control signal includes first signal EN (curves 1206a,
1206b, 1206c shown in FIGS. 10, 11A-11C and 12A-12C). In some
embodiments, the at least one control signal includes read word
line signal RWL (curve 1402 in FIGS. 13A-13B and 14A-14B) or the
signal on data node C of cross-coupled inverters 302 (curve 1406b
shown in FIG. 14B).
Method 1500 continues with operation 1506 in which the voltage
control unit selectively adjusts a voltage signal in response to
the at least one control signal. In some embodiments, the voltage
signal comprises a first voltage signal or a second voltage signal.
In some embodiments, selectively adjusting the voltage signal
comprises selectively adjusting a voltage signal on a word line
connected to the at least two p-type pass gates. In some
embodiments, selectively adjusting the voltage signal comprises
selectively adjusting a first voltage signal on a bit line
connected to the memory cell and selectively adjusting a second
voltage signal on a bit line bar connected to the memory cell.
In some embodiments, the voltage signal includes boosted voltage
signal BVDD (curve 408 shown in FIG. 4) or bit line signal BL/bit
line bar BLB (curves 410a, 410b shown in FIG. 4). In some
embodiments, the voltage signal includes second voltage signal CVSS
(curves 706a, 706b shown in FIG. 7A-7B). In some embodiments, the
voltage signal includes the signal on data nodes C/T of
cross-coupled inverters 302 (curves 708a, 708b, 710a, 710b shown in
FIGS. 7A-7B). In some embodiments, the voltage signal includes
negative word line signal NVSS (curve 908 in FIGS. 8A-8B and 9) or
word line signal WL/RWL (curve 902 in FIGS. 8A-8B and 9). In some
embodiments, the voltage signal includes word line signal WL/RWL
(curves 1206a, 1206b, 1206c shown in FIGS. 10, 11A-11C and
12A-12C), write word line signal WWL/RWL (curve 1404b shown in FIG.
14B), the signal on data node C of cross-coupled inverters 302
(curve 1406b shown in FIG. 14B) or read bit line signal RBL (curve
1412b shown in FIG. 14B).
In some embodiments, the memory cell is a single-port memory cell,
e.g., single-port memory cell 300a (FIG. 3A). In some embodiments,
the memory cell is a two-port memory cell, e.g., two-port memory
cell 300b (FIG. 3B). In some embodiments, the memory cell is a
dual-port memory cell, e.g., dual-port memory cell 300c (FIG.
3C).
One of ordinary skill in the art would recognize that operations
are able to be removed or that additional operations are able to be
added to method 1500 without departing from the scope of this
description. One of ordinary skill in the art would also recognize
that an order of operations in method 1500 is able to be adjusted
without departing from the scope of this description.
One aspect of this description relates to a static random access
memory (SRAM). The SRAM includes a memory cell comprising at least
two p-type pass gates. The SRAM also includes a first data line
connected to the memory cell, a second data line connected to the
memory cell and a voltage control unit connected to the first data
line, wherein the voltage control unit is configured to control the
memory cell.
Another aspect of this description relates to a semiconductor
device including a static random access memory (SRAM). The SRAM
includes a memory cell comprising at least two p-type pass gates.
The SRAM also includes a bit line connected to the memory cell, a
bit line bar connected to the memory cell, a word line connected to
the memory cell and a voltage control unit connected to the memory
cell, wherein the voltage control unit is configured to control the
memory cell.
Still another aspect of this description relates to a method of
controlling a static random access memory (SRAM). The method
includes pre-charging at least one data line to a reference
voltage, wherein the at least one data line is connected to a
memory cell, wherein the memory cell comprises at least two p-type
pass gates, activating a voltage control unit connected to the at
least one data line, wherein the activating the voltage control
unit comprises receiving at least one control signal and
selectively adjusting a voltage signal in response to the at least
one control signal.
The foregoing outlines features of several embodiments so that
those of ordinary skill in the art may better understand the
aspects of the present disclosure. Those of ordinary skill in the
art should appreciate that they may readily use the present
disclosure as a basis for designing or modifying other circuits,
processes and structures for carrying out the same purposes and/or
achieving the same advantages of the embodiments introduced herein.
Those of ordinary skill in the art should also realize that such
equivalent constructions do not depart from the spirit and scope of
the present disclosure, and that they may make various changes,
substitutions, and alterations herein without departing from the
spirit and scope of the present disclosure.
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